The lifetime in months of a transistor in a certain application is random with probability density function:

f(x) = {0.4e^-0.4x, x> 0 0, x< 0

a. compute the mean lifetime.
b. compute the standard deviation of the lifetimes.
c. compute the cumulative distribution function of the lifetime.
d. compute the probability that the lifetime will be less than 6 months.
e. compute the 60^th percentile of the lifetime.

Afarmer sells 9.5 kilograms of apples and pears at the farmer's market. 4/5 of the weight is the apples and the rest is the pears. how many kilograms of pears did she sell at the farmers market

Isuck at math ; ^; m a student solved this problem and said the answer is 3 feet. chase had a roll of ribbon that contained 7 7/8  feet of ribbon. he cut off one piece that was 3 5/8  feet long and another piece that was 1 1/4  feet from the roll. how much ribbon was left on the roll? is the student's answer reasonable? yes, the answer is reasonable. no, the answer is not reasonable. it should be about 2 feet. no, the answer is not reasonable. it should be about 13 feet. no, the answer is not reasonable. it should be about 4 feet.

How do i put 3(x+7) in distributive property