I have determd. the prob of sucsful calls is 35%. what's min no I must make to be 99% sure of successful call

Question

Help! Over the past years, I have determined that the probability of a successful sales call is 35%. What is the minimum number of sales call I must make to be at least 99% sure of making at least one sales? I'm stuck on this problem. Help, please.

Answer 1

0.01 = (1 - 0.35)^n = (0.65)^n
ln(0.01) = n*ln(0.65)
n = ln(0.01)/ln(0.65)
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Had to find my calculator...n = 10.7 so, 11 tries.