a,b. Z = (score-mean)/SD
Find table in the back of your statistics text labeled something like "areas under normal distribution" to find the proportion/probability for the Z score. Multiply by 100.
c. Find table in the back of your statistics text labeled something like "areas under normal distribution" to find the proportion/probability (.90) and its Z score insert into equation above.
Suppose that the amount of time it takes the IRS to refund to taxpayers is normally distributed with a mean of 12 weeks and a variance of 9.
a. What percent of taxpayers should get a refund within 5 weeks?
b. What percent of taxpayers will get their refund within 10-15 weeks?
c. How long will it be before 90% of the taxpayers get their refund?
d. If 10 independent taxpayers filed their refunds on the same day, what is the probability that at least 7 will get their refunds within 5 weeks?
e. What is the probability that the average time to get the refund for these 10 taxpayers (in c) is more than 13 weeks? (Not required. Bonus points if solved correctly.)
1 answer
1 answer