Which value do I use to solve this stats problem?

Question

At a shelter housing there are125 kitties and doggies, the probability if any one orphaned creature to be adopted within two weeks is 0.35.

a) what is the probability of exactly 50 creatures to be adopted within two weeks?

b)what is the probability of at least 50 creatures to be adopted within two weeks?

Answer 1

What you want is the binomial distribution with the probability p of an animal being adopted within two weeks is 0.35. (Think of each animal has being a biased coin tossed once every two weeks.)

http://en.wikipedia.org/wiki/Binomial_distribution

for part b, I'd use the normal approximation to the binomial distribution

http://en.wikipedia.org/wiki/Normal_distribution

convert the boundary value of 50 creatures to the number of standard deviations above the mean and go on from there.