Question: Empire Electronics manufactures a compact microwave oven; one of it chief component parts, a magnetron tube has a mean lifespan of 6.25 years. The store has promoted a five year warranty on this household appliance, which includes this component part.

a) What percentage of all its magnetron tubes in these microwaves should Empire expect to need to replace during the warranty period?

b) What percentage of microwaves experiences a failure by their magnetron tubes as early as 7 years but no later than 10 years after date of purchase?

c) XC: Determine the variance for this continuous random variable. [COMMENTS & HINTS: This question is for bonus credit only. If necessary, research how to compute this parameter.]