I do not know how to start this problem-help needed-kindly help me
- The lifetimes of a colour TV picture tube is normally distributed, with a mean of 8 yrs and a standard deviation of 2 years.
(i) What is the probability that a picture tube will last more than 10 yrs?
(ii) If the firm guarantees the picture tube for 4 yrs, what percentage of the tubes sold will have to be replaced?
Hint: for i, you need the lifetime to be more than one standard deviation high. for ii, it needs to be more than 2 standard deviations low.