binomial experiment, probability

Question

according to a report of the Nielsen company 65% of internet searches in may 2010 used the google search engine. Assume that sample of 20 searches is studied.

 

a) What is the probability that exactly 16 of them used goole?

b) what is the probability that more than 16 of them used google?

c) what is the probability that between 15 and 18, inclusive used google?

 

Answer 1

Katy,

 

a) Use the binomial distribution formula:  C(20,16)*(0.65)^16*(0.35)^4

b) Sum the terms for 17,18,19 and 20 outcomes out of 20 with probability 0.65: C(20,17)*(0.65)^17*(0.35)^3+....

c) Sum the terms you already calculated for 16 and 17 outcomes