Poll
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49 members have voted
Same scenario, but what’s the expected waiting time for:Quote: Ace2Your email account receives an average of one email every six minutes, following the exponential distribution. At t=0 minutes, you open your inbox and record the exact amount of time it takes to receive a new email
Starting at t=1 minute, you roll a single six-sided die every minute until you roll a 4. So the sixth roll (if necessary) will occur at t=6 minutes.
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1) the first event (email or 4) to happen?
2) both events (email and 4) to happen at least once ?
Quote: Ace2
Same scenario, but what’s the expected waiting time for:
1) the first event (email or 4) to happen?
2) both events (email and 4) to happen at least once ?
link to original post
I want to say
but I'm not sure
Disagree. 36/11 would be the expected waiting time of rolling two dice until a 4 appears on one(or both).Quote: SkinnyTonyQuote: Ace2
Same scenario, but what’s the expected waiting time for:
1) the first event (email or 4) to happen?
2) both events (email and 4) to happen at least once ?
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I want to say36/11 and 102/11
but I'm not sure
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102/11 would be the expected waiting time of rolling two dice until a 4 appears on one (or both), then opening the email account and adding the time needed to receive the next message. 102/11 would also be the expected waiting time of rolling two dice until a 4 appears on one (or both), then rolling a single die until a 4 appears
Anyone working on this or should I post the answer?Quote: Ace2Same scenario, but what’s the expected waiting time for:Quote: Ace2Your email account receives an average of one email every six minutes, following the exponential distribution. At t=0 minutes, you open your inbox and record the exact amount of time it takes to receive a new email
Starting at t=1 minute, you roll a single six-sided die every minute until you roll a 4. So the sixth roll (if necessary) will occur at t=6 minutes.
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1) the first event (email or 4) to happen?
2) both events (email and 4) to happen at least once ?
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1) The general solution (f) is:Quote: Ace2Anyone working on this or should I post the answer?Quote: Ace2Same scenario, but what’s the expected waiting time for:Quote: Ace2Your email account receives an average of one email every six minutes, following the exponential distribution. At t=0 minutes, you open your inbox and record the exact amount of time it takes to receive a new email
Starting at t=1 minute, you roll a single six-sided die every minute until you roll a 4. So the sixth roll (if necessary) will occur at t=6 minutes.
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1) the first event (email or 4) to happen?
2) both events (email and 4) to happen at least once ?
link to original post
link to original post
f = (1 - 1/e^(1/6))m + (1 + 5/6f)/e^(1/6)
This expresses the probability that an email was received within one minute times the average time needed for an email to be received (m)...assuming it was received in the first minute...plus the probability an email was not received within one minute times one minute plus 5/6 chance a 4 is not rolled and the another iteration begins
(m) is calculated by taking the derivative of 1/e^(x/6), multiplying by x and dividing by the probability of not receiving an email within one minute to get the function: x/[6e^(x/6)(1 - 1/e^(1/6)]. Then take the integral with respect to x of that function from 0 to 1 to get (m) = (6e^(1/6) - 7)/(e^(1/6) - 1) =~0.486
Plug m into the first formula and solve for f to get the answer of:
[(6e^(1/6) - 7)/(e^(1/6) - 1)*(1 - 1/e^(1/6)) + 1/e^(1/6)]/(1 - 5/6*1/e^(1/6))
=~ 3.127 minutes
2) Let p= 1/(6e^(1/6) - 5) =~ 0.479 be the probability that a 4 is rolled before an email is received. The general solution is :
f + p6 + (1-p)(6-m)
This expresses the average time needed for the first event to happen (f) plus the chance the 4 was rolled first times six (the average time for the next email to arrive is always six minutes) plus the chance an email was received first times six minus the average time it took to receive the email. Plug in f,p and m to get
[(6e^(1/6) - 7)/(e^(1/6) - 1)*(1 - 1/e^(1/6)) + 1/e^(1/6)]/[1 - 5/6*1/e^(1/6)]+ 12/(6e^(1/6) - 5)
=~ 8.87 minutes
There's a slicker way to get this answer via inclusion-exclusion. Looking at the email and die separately, it will take an average of six minutes for each to occur. Take six minutes times two minus the time spent waiting for either, so : 6*2 - f =~ 8.87 minutes
I verified both answers to three digits with numerical integrations in excel at 1/1000 spacing
Until now I cannot find a way to directly calculate the variance, though numerical integration in excel tells me it's about 8.23 for the first event to happen. The combination of discrete (die) and continuous (email) variables invalidates every calculation method I know
Incidentally, setting the average email arrival time to 1/ln(7/6) =~ 6.49 minutes would give the two events an equal chance of happening first
Quote: AnotherBillAm I the only one who feels like my head is about to explode?
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I'm not sure I would call this "easy". Basically if I have to break out pencil and paper I lose interest. Yes I'm lazy.
I guess I prefer the kind of puzzle that's "clever", where, when you see the trick and have the "aha" moment, the solution becomes obvious with minimal computation that you can do in your head. To me that's the difference between a puzzle and a homework question. I'm too old for homework.
There are several tricks and “aha” moments in that solution. Initially I thought it could not be solved until I took the derivative of 1/e^(x/6) times x then integrated from 0 to 1 to get the average waiting time for the email between 0 and 1. The inclusion-exclusion solution to #2 is one of the more clever parts of the solutionQuote: SkinnyTonyQuote: AnotherBillAm I the only one who feels like my head is about to explode?
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I'm not sure I would call this "easy". Basically if I have to break out pencil and paper I lose interest. Yes I'm lazy.
I guess I prefer the kind of puzzle that's "clever", where, when you see the trick and have the "aha" moment, the solution becomes obvious with minimal computation that you can do in your head. To me that's the difference between a puzzle and a homework question. I'm too old for homework.
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This is definitely not the first problem on this thread that pushes the boundaries of “easy”. The solutions to this one seem more complex than they really are because they combine multiple constants
Quote: Ace2There are several tricks and “aha” moments in that solution. Initially I thought it could not be solved until I took the derivative of 1/e^(x/6) times x then integrated from 0 to 1 to get the average waiting time for the email between 0 and 1. The inclusion-exclusion solution to #2 is one of the more clever parts of the solutionQuote: SkinnyTonyQuote: AnotherBillAm I the only one who feels like my head is about to explode?
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I'm not sure I would call this "easy". Basically if I have to break out pencil and paper I lose interest. Yes I'm lazy.
I guess I prefer the kind of puzzle that's "clever", where, when you see the trick and have the "aha" moment, the solution becomes obvious with minimal computation that you can do in your head. To me that's the difference between a puzzle and a homework question. I'm too old for homework.
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This is definitely not the first problem on this thread that pushes the boundaries of “easy”. The solutions to this one seem more complex than they really are because they combine multiple constants
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Don't get me wrong, I think it's an interesting question. But definitely not easy. I'm sure that there are others in the thread that aren't easy; I didn't mean to single this question out. It was just a response to the question about the head exploding.
The rest is just my personal preference. I find computation to be tedious; I always have. This is why I always focused on abstract algebra and graph theory in school and steered clear of statistics (which I wish I had studied more because it's really useful), calculus, and anything that used numbers other than 0 and 1.
Quote: Ace2
1) the first event (email or 4) to happen?
2) both events (email and 4) to happen at least once ?
link to original post
(6-35*EXP(-1/6)/6)/(1-5*EXP(-1/6)/6) =~ 3.605550308
5*(5/6)*EXP(-1/6)/(1-(5/6)*EXP(-1/6))^2 =~40.639195
That feels too long to me, but it's what I get. I've never been much afraid of being wrong here.
Disagree with both. I’m confident with both of the answers I posted. As mentioned, I confirmed them with numerical integrations.Quote: Wizard
5*(5/6)*EXP(-1/6)/(1-(5/6)*EXP(-1/6))^2 =~40.639195
That feels too long to me, but it's what I get. I've never been much afraid of being wrong here.
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Your second answer of 40.6 isn’t reasonable. If you did the events sequentially (start rolling the die after an email is received or check email account after a 4 is rolled), the expected waiting time for both to occur should be 6 + 6 =12 minutes. So if the events go concurrently, the time for both to happen must be less than that and a good estimate would be 6/2 + 6 =9, which is actually quite close to the answer of ~8.87 minutes
Quote: Ace2Disagree with both.
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I was pretty confident with #1, but know I am not embarrassed to be wrong. The second I shouldn't have posted -- it was more of a progress report.
The expected time in the first minute is the integral from 0 to 1 of exp(-x/6) = 6(1-exp(-1/6))
The expected added time for the first die roll to be a 4 is exp(-1/6)*(1/6).
The probability of neither event happening is exp(-1/6)*(5/6).
Let the answer be x. Construct as:
x = 6(1-exp(-1/6)) + exp(-1/6)*(1/6) + exp(-1/6)*(5/6) * x
Then solve for x.
Based on what? Do you have a simulation and/or numerical integration that confirms your answer ?Quote: Wizard
I was pretty confident with #1
Quote: Ace2Based on what? Do you have a simulation and/or numerical integration that confirms your answer ?
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Based on the argument in my spoiler tag.
All even-numbered people say, "Everyone in front of me is a liar."
All odd-numbered people say, "Everyone behind me is a liar."
Who is telling the truth?
Quote: charliepatrickI get that #2 and #49 have to tell the truth since they will be referring to #1 and #50, who are actually lying.
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I agree!
[spoiler=problem 1]
1 2 4 24 47 48 49;
3 5 6 26 44 45 46;
7 11 9 22 41 42 43;
10 8 12 28 38 39 40;
13 14 17 23 35 36 37;
16 15 18 27 32 33 34;
19 20 21 25 29 30 31.
Part 2 The objective at this stage is to [net] add 25 to each pile using the 22, 23, 24, 25, 26, 27 and 28 coins.
So add the 28 coin to pile 3 and remove the "3" and add it with the "22". Similarly for 27/2 and 26/1. Thus the first three piles have had 25 added to them. The last four piles can each have a 25 added, either being 25, 24+1, 23+2 or 22+3.
After these two parts the piles, which had 150gm, then had [a net of] 25 grams added to each. Thus they now each weigh 175gm. Note 7*175 is the same as 1225, which is the total of 1 thru 49.
The mathematics is that the entries are A, A+1, ... A+6 where A=1, B=8 etc. and each column gets +0, +1, +2... +6. so the total for each column is A+B+C+D+E+F+G+0+1+2+3+4+5+6. For instance column 1 has A, B+6, C+5...G+1.

Coin | Son |
---|---|
1 | 1 |
2 | 2 |
3 | 3 |
4 | 4 |
5 | 5 |
6 | 7 |
7 | 6 |
8 | 6 |
9 | 4 |
10 | 5 |
11 | 1 |
12 | 2 |
13 | 3 |
14 | 7 |
15 | 7 |
16 | 6 |
17 | 3 |
18 | 5 |
19 | 2 |
20 | 4 |
21 | 1 |
22 | 1 |
23 | 2 |
24 | 3 |
25 | 4 |
26 | 5 |
27 | 7 |
28 | 6 |
29 | 7 |
30 | 6 |
31 | 5 |
32 | 4 |
33 | 3 |
34 | 2 |
35 | 1 |
36 | 1 |
37 | 2 |
38 | 3 |
39 | 4 |
40 | 5 |
41 | 7 |
42 | 6 |
43 | 7 |
44 | 6 |
45 | 5 |
46 | 4 |
47 | 3 |
48 | 2 |
49 | 1 |
I got the puzzle from one of my favorite YouTube channels, Mind Your Decisions. It's puzzle 6 in the prior link.
Presh goes over two methods to construct Magic Squares of odd sides.
Quote: WizardA king has 49 gold coins. The coins weigh 1, 2, 3, ... 49 grams each. How can he divide them among seven sons so that each son gets seven coins such that the sum of the weights is equal?
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1 | 2 | 3 | 4 | 5 | 6 | 7 |
---|---|---|---|---|---|---|
8 | 9 | 10 | 11 | 12 | 13 | 14 |
15 | 16 | 17 | 18 | 19 | 20 | 21 |
22 | 23 | 24 | 25 | 26 | 27 | 28 |
29 | 30 | 31 | 32 | 33 | 34 | 35 |
36 | 37 | 38 | 39 | 40 | 41 | 42 |
43 | 44 | 45 | 46 | 47 | 48 | 49 |
1 + 9 + 17 + 25 + 33 + 41 + 49 = 175
8 + 16 + 24 + 32 + 40 + 48 + 7 = 175
15 + 23 + 31 + 39 + 47 + 6 + 14 = 175
22 + 30 + 38 + 46 + 5 + 13 + 21 = 175
29 + 37 + 45 + 4 + 12 + 20 + 28 = 175
36 + 44 + 3 + 11 + 19 + 27 + 35 = 175
43 + 2 + 10 + 18 + 26 + 34 + 42 = 175
P.S.: Am I the only one whose URLs (image tags or whatever) get cut and broken when trying to post them on this forum?
Quote: AnotherBill
P.S.: Am I the only one whose URLs (image tags or whatever) get cut and broken when trying to post them on this forum?
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Welcome to the forum. You're the first one I've heard to mention it.
Quote: WizardQuote: AnotherBill
P.S.: Am I the only one whose URLs (image tags or whatever) get cut and broken when trying to post them on this forum?
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Welcome to the forum. You're the first one I've heard to mention it.
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Thank you!
I sent a private message to JB about a week ago but didn't get any response.
Any URL address I try to post on the forum (in or not in tags) just gets truncated. For example, https_COLON_SLASH_SLASH_example_DOT_com_SLASH_blablabla (changed actual colons, dots, and slashes) gets truncated to _SLASH_blablabla. Checked in Opera and Firefox. OS is Ubuntu 24.04.
P.S.: Note the typical link to original post in my messages. There is no hyperlink as it should be… At least, it's not shown to me.
I suspect a while ago there was a problem in that bots kept posting links to various sites or just placing spamming adverts. These used to have to be removed my moderators. So my guess is perhaps the system now automatically updates any URLs until a member reaches some threshold.
Quote: AnotherBill
I sent a private message to JB about a week ago but didn't get any response.
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I'm curious how a new member would know about JB. Anyway, he hasn't been heard from in years. I hope he's okay.
Yes, we had to do some screening recently due to a spam attack. Maybe that has something to do with it. Also, as a new member, you can't post links, which may muddy the waters.
Quote: WizardI'm curious how a new member would know about JB. Anyway, he hasn't been heard from in years. I hope he's okay.link to original post
JB is the author of the "Formatting Codes" thread and is an administrator (if to believe the information provided there). That's why I decided to reach him out.
Quote: AnotherBillQuote: WizardQuote: AnotherBill
P.S.: Am I the only one whose URLs (image tags or whatever) get cut and broken when trying to post them on this forum?
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Welcome to the forum. You're the first one I've heard to mention it.
link to original post
Thank you!
I sent a private message to JB about a week ago but didn't get any response.
Any URL address I try to post on the forum (in or not in tags) just gets truncated. For example, https_COLON_SLASH_SLASH_example_DOT_com_SLASH_blablabla (changed actual colons, dots, and slashes) gets truncated to _SLASH_blablabla. Checked in Opera and Firefox. OS is Ubuntu 24.04.
P.S.: Note the typical link to original post in my messages. There is no hyperlink as it should be… At least, it's not shown to me.
link to original post
This is part of the anti-spam system.
New forum members are put on an initial probation period until "good standing" is established. During that probation, links and images are confounded.
This is deliberate. (It's not a bug, it's a feature.) To the best of my knowledge, no admin is able to abbreviate to probationary period.
Quote: Dieter
This is part of the anti-spam system.
New forum members are put on an initial probation period until "good standing" is established. During that probation, links and images are confounded.
This is deliberate. (It's not a bug, it's a feature.) To the best of my knowledge, no admin is able to abbreviate to probationary period.
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Dieter, thank you for your explanation!
By the way, it looks like new forum members are allowed to use links in private messages. Because, when I was writing a private message to JB, I was able to insert an image.
Direct: https://www.youtube.com/watch?v=cpwSGsb-rTs.
Quote: WizardHowever, I claim the answer presented is wrong, based on how it is phrased.
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Do you mean the narrator didn't say the you're 100% sure the sound was uttered by one of those frogs?
Quote: AnotherBillDo you mean the narrator didn't say the you're 100% sure the sound was uttered by one of those frogs?
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No, that's not my issue with the wording. My issue is that not every male necessarily croaks all the time. In other words, the fact that only males croak doesn't mean every male croaks loudly enough to be heard.
To put it another way, I think you're more likely to hear croaking from two males than one male.
Quote: WizardQuote: AnotherBillDo you mean the narrator didn't say the you're 100% sure the sound was uttered by one of those frogs?
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No, that's not my issue with the wording. My issue is that not every male necessarily croaks all the time. In other words, the fact that only males croak doesn't mean every male croaks loudly enough to be heard.
To put it another way, I think you're more likely to hear croaking from two males than one male.
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So what you're saying is: the wording is a bit amphibious?
Quote: AutomaticMonkeySo what you're saying is: the wording is a bit amphibious?
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Ha! Couldn't have said it better myself.
Quote: avianrandyFor the math nerds on here,in roman numerals if a line is placed above a letter it's value is increased by what?
answer given was 1,000. This surprisee as their is already for 1000 which is m. Would love to know more about this.
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The vinculum (bar) multiplies by 1000. This is different from the M, which adds 1000.
So, for example, to write the number one million, you could write 1000 Ms, or a single M with a vinculum over it.
Quote: WizardTo put it another way, I think you're more likely to hear croaking from two males than one male.
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Synchronous croaking (to give the impression of a single frog croaking)?
Quote: SkinnyTonyQuote: avianrandyFor the math nerds on here,in roman numerals if a line is placed above a letter it's value is increased by what?
answer given was 1,000. This surprisee as their is already for 1000 which is m. Would love to know more about this.
link to original post
The vinculum (bar) multiplies by 1000. This is different from the M, which adds 1000.
So, for example, to write the number one million, you could write 1000 Ms, or a single M with a vinculum over it. Thank you very much skinnytony. This makes perfect sense. An m with a bar over it to you as thanks
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