Question

8. A manufacturing company of light bulb claims that an average light bulb lasts 500 days. A contractor randomly selects 30 bulbs for testing. The sampled bulbs last an average of 490 days, with a standard deviation of 100 days. If the claim were true, what is the probability that 30 randomly selected bulbs would have an average life of no more than 490 days? [10]

Answer 1

Value is obtained from standard normal table

Given M = 500 T = 100 n -30 if clain is true u=500 To find P(* <490) we know that X follow Normal (ui X n Normal ( 500, 100 130 100/130 P( X <490) = P(X - 5Do < 490-500 100/180 미 <-0.55) 0.2912 z from Normal distribution table