Need help on stats question!

Suppose you want to eat lunch at a popular restaurant. The restaurant does not take reservations, so there is usually a waiting time before you can be seated. Let x represent the length of time waiting to be seated. From past experience, you know that the mean waiting time is μ = 17.4 minutes with σ = 4.3 minutes. You assume that the x distribution is approximately normal. (Round your answers to 4 decimal places.)


(a) What is the probability that the waiting time will exceed 20 minutes, given that it has exceeded 15 minutes? Hint: Compute P(x > 20|x > 15).


(b) What is the probability that the waiting time will exceed 25 minutes, given that it has exceeded 18 minutes? Hint: Compute P(x > 25|x > 18).

Hi,

(a) What is the probability that the waiting time will exceed 20 minutes, given that it has exceeded 15 minutes? Hint: Compute P(x > 20|x > 15).

On the TI-83:

normalcdf(15,100,17,4,4.3) = .7116

normalcdf(20,100,17,4,4.3) = .2727

P(x > 20|x > 15) = .2727/.7116 = .3832 <==ANSWER



(b) What is the probability that the waiting time will exceed 25 minutes, given that it has exceeded 18 minutes? Hint: Compute P(x > 25|x > 18).

On the TI-83:

normalcdf(18,100,17,4,4.3) = .4445

normalcdf(25,100,17,4,4.3) = .0386

P(x > 20|x > 15) = .0386/.4445 = .0868 <==ANSWER

I hope that helps!! :-)