"Recommend a Friend for a Bonus Entry"

I'm a bit confused about this.

Often when I enter competitions online, they'll tell you that you'll get a bonus entry for each friend you refer.

Say I'm the only person who enters - I have 100% chance of winning. If I recommend a friend, I then have 66.6% chance of winning, my friend 33.3%.

I figure that it is NEVER worthwhile recommending a friend for a bonus entry as your friend's entry then cancels out your bonus entry, but then, it seems to swing a bit in your favour as the number of entries increases. Logically my head says 'don't do it'... mathematically?

Yeah, but how likely is it that you get an entry to an empty competition? If it was 'somehow' quite probable that you'd get to "automatically win" by being the only person entered, then it wouldn't be worth referring friends... Unless you talk to your friends before hand and tell them you'll give them a cut of X (referral bonus) if you can use their info.

Quote: supahstarsarah

Say I'm the only person who enters - I have 100% chance of winning. If I recommend a friend, I then have 66.6% chance of winning, my friend 33.3%.

Yes, BUT - you will never be the only entrant.

Realistically, there will be at least 1000 entrants. Suppose 999 have entered before you.

When you enter, your chances of winning a fair random draw are 1/1000. Once your referred friend enters, you're up to 2/1001 - almost twice as likely to win, plus that 1/1001 warm fuzzy feeling if your friend wins.