I need help with probability problems in statistics.?

Replacement times for new Ford Taurus GL automobiles are normally distributed with a mean of 7.1 years and a standard deviation of 1.4 years. Find the probability that seven randomly selected Taurus GL automobiles will have a mean replacement time greater than 7.0 years.


Among U.S. households, 24% have telephone answering machines. If a telemarketing campaign involves 2,500 households, find the probability that more than 650 have answering machines.

Find the z score for 7 years. (7 - 7.1)/(1.4)

Then look at your z score table, find the area, and subtract from 1. The subtraction is necessary because the table will give you the "less than" probabilities, and you want greater than.

24% of 2500 will be 600. The procedure will be the same as for the car, but instead of a standard deviation you'll use an expression that uses the proportion of households (24%)

That expression will be square root(p(1-p)/n) where p is your percent (change it to a decimal) and n is your sample size.

TMFH[too many for help}