A Christmas tree light has an expected life of 180 hr and a standard deviation of 2 hr.
(a) Find a bound on the probability that one of these Christmas tree lights will require replacement between 170 hr and 190 hr. (Enter your answer to two decimal places.)

(b) Suppose a large city uses 170,000 of these Christmas tree lights as part of its Christmas decorations. Estimate the number of lights that are likely to require replacement between 160 hr and 200 hr of use.

Question

A Christmas tree light has an expected life of 180 hr and a standard deviation of 2 hr.
(a) Find a bound on the probability that one of these Christmas tree lights will require replacement between 170 hr and 190 hr. (Enter your answer to two decimal places.)


(b) Suppose a large city uses 170,000 of these Christmas tree lights as part of its Christmas decorations. Estimate the number of lights that are likely to require replacement between 160 hr and 200 hr of use.