A few days ago
savspringer

probability question! Please Help!?

AT&T claims that when customers call directory assistance for telephone numbers, the right number is given 90% of the time. Assume 90% rate of correct responses. What is the probability that among 5 requests, 3 of them are correct? (Adapted from Triola, 2000)

Top 2 Answers
A few days ago
Mitch

Favorite Answer

Use the binomial formula:

(p + q)^5 =

p^5 + 5p^4q + 10p^3q^2 + 10p^2q^3 + 5pq^4 + q^5

p = .90

q = .10

P(3) = 10p^3q^2

P(3) = 10 * (.9)^3(.1)^2

P(3) = 10 * (.729) * (.01) = .0729 or 7.29%

Good luck in your studies,

~ Mitch ~

This website will calculate the probabilities for you:

http://stattrek.com/Tables/Binomial.aspx

There’s also a powerpoint file covering this problem:

http://staff.wtn.k12.sd.us/fairchis/powerpoints/book%204-3.ppt

0

A few days ago
Anonymous
If for sure 90 is the rate of correct reponses then theoretically the probability is 100% – THEORETICALLY. This is because 90% of 5 is 4.5 and 4.5 < 3 which means that, because the rate of correct answers is 90% the probabilty of any percentage of 5 under 90% being correct is 100%. So that is your answer.
0