Question

Let x be the number of successes throughout n independent repetitions of a random experiment having probability of success p=1/4. determine the smallest value of n so that p(1<=x)>=0.7

Answer 1

To answer problems like this you have to use binomial:

P (x > 1) = 1 – p (0 < x < 1) > .7

So:

1 – p (0) – p (1) > .7

1 – (3/ 4) ^n – (3/ 4) ^n (n – 1 ) (1/ 4) > .7

Therefore n > 5.185, and the smallest value of n so that we can satisfy the given condition is 6 (rounded up)