Consider this game:
You have a 1% chance of winning on the first try. If you win, great!
If you don't, win on the first try, you have a 2% chance of winning on the second try.
If needed you have a 3% chance on the third try and so on until you eventually win.
What is the expected number of tries to win this game?
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As I usually do with such problems, I'll start with simpler problems and look for a pattern. Maybe even a formula. Maybe a sequence in the OEIS.
Call the problem sought n=100 and I'll start with n=2: A 1/2 chance of winning and a 2/2 chance of winning if a second try is needed. E.V. = 1/2 * 1+1/2 * 2=3/2=1.5
n=3. 1st try: 1/3, 2nd try 2/3 * 2/3, 3rd try 2/3 * 1/3 * 3/3. E.V. = 1/3 * 1+4/9 * 2+4/9 * 3=17/9=.38888
n=4. 1st try: 1/4, 2nd try 3/4 * 2/4, 3rd try 3/4 * 2/4 * 3/4, 4th try 3/4 * 2/4 * 1/4 * 4/4, E.V.= 1/4 * 1+6/8 * 2 +18/64 * 3+6/64 * 4 = 71/32 = 142/64
n=5. Long story short E.V. = 1569/5^4
Ok so the denominators are n^(n-1) and the numerators, beginning the n=1 are 1,3,17,142,1569
A single hit in OEIS and the formula is there as a summation. The numbers are going to get huge but there's a link to the first 380 terms. I need the 100th.
1 2 2 0 9 9 6 0 6 3 0 2 1 5 9 8 0 3 0 0 2 5 3 1 3 2 9 5 6 8 1 5 0 1 2 9 9 8 4 1 2 7 1 4 1 5 9 3 9 2 6 6 2 2 2 3 8 5 4 9 9 2 5 2 1 1 2 8 8 0 9 3 7 4 8 2 2 8 9 6 6 0 6 8 7 9 0 6 2 7 9 3 5 6 5 7 5 6 4 8 0 0 7 7 4 3 1 1 6 8 6 9 4 6 4 2 7 9 4 5 5 2 7 9 8 9 3 4 3 6 6 6 9 4 5 7 7 2 5 3 5 7 3 0 1 3 7 3 5 4 2 1 8 4 3 8 4 5 9 5 7 0 4 3 3 0 6 7 2 6 3 0 9 2 3 2 6 4 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 ≈ 1 . 2 2 0 9 9 6 0 6 3 0 2 ∗ 1 0 1 9 9
So the answer is 1 0 0 9 9 1 . 2 2 0 9 9 6 0 6 3 0 2 ∗ 1 0 1 9 9 = 1 2 . 2 0 9 9 6 0 6 3 0 2