4. The life spans of trucks manufactured by company A are normally distributed with

a mean of 10 years and variance of 25 years.

[10 Marks]

a) What is the probability that a random truck bought from company A will have a

life span of more than 12 years?

b) What is the probability that a random truck bought from company A will have a

life span of less than 7 years?

c) What is the probability that a truck randomly bought from company A will have

a life span of more than 5 years but less than 25 years