Math Help - help with homework

1. help with homework

I have a homework question I can't figure out for the life of me.

1. A state senator believes that 25% of all senators on the committee will support his tax proposal. Suppose that this is correct and that 5 senators are approached at random.

A) What is the probability that at least 1 senator will agree

B) What is the probability that a majority of the 5 will strongly support the proposal?

I tried the formula p(x)=n!/x!(n-x)! (times) p^x (times) (1-p)^n-x
which led me to p(x)=5!/(1!95-1)! (times) .25^1 (times) (1-.25)^4
and this gave me .3955 and I know it's wrong ( I looked at the answer in the back of the book) Can someone please help me.

2. Originally Posted by jbeatons
I have a homework question I can't figure out for the life of me.

1. A state senator believes that 25% of all senators on the committee will support his tax proposal. Suppose that this is correct and that 5 senators are approached at random.

A) What is the probability that at least 1 senator will agree

B) What is the probability that a majority of the 5 will strongly support the proposal?

I tried the formula p(x)=n!/x!(n-x)! (times) p^x (times) (1-p)^n-x
which led me to p(x)=5!/(1!95-1)! (times) .25^1 (times) (1-.25)^4
and this gave me .3955 and I know it's wrong ( I looked at the answer in the back of the book) Can someone please help me.
You need the binomial cdf, meaning you need to sum that formula for different values of x, in part B, x=3, x=4, x=5

For part A, P(at least 1)=1-P(none)= $1-.75^5$