the manufacturer of a certain brand of light bulb claim that the variance of the lives of these bulb is 4200 square hours.a consumer agency took a...

the manufacturer of a certain brand of light bulb claim that the variance of the lives of these bulb is 4200 square hours.a consumer agency took a random sample of 25 such bulb and tested them. the variance of he lives of these bulb was found to be 5200 square hours. assume that the lives of all such bulb (approximately) normally distribution.a) make the 99% confidence intervals for the variance and standard deviation of the lives of all such bulbs.b) test at the 5% significant level whether the variance of such bulbs is different from 4200 square hours.