binomial problem: computing prob. of receiving 1 wrong reply

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serenity26

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An article in USA Today stated that "Internal surveys paid for by directory assistance providers show that even the most accurate companies give out wrong numbers 25% of the time." Assume that you are testing such a provider by making 10 requests and also assume that the provider gives the wrong telephone number 25% of the time. Find the probability of getting at most, one wrong number.

i figureout that i'm suppose to use the binomial formula. and n =10 p=.75 q=.75 and x=1 but when i plug the numbers in i got it wrong please help
 
You must account for 0 wrong numbers and 1 wrong number. The problem says at most one.

\(\displaystyle \L\\\displaystyle\sum_{k=0}^{1}C(10,k)(0.25)^k(0.75)^{10-k}\)
 
Do your binomial thing, except do it for 0 and 1, then add them.
 
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