SGO Corporation manufactures light bulbs The CEO claims that

SGO Corporation manufactures light bulbs. The CEO claims that an average light bulb lasts 280 days. The population standard deviation is known to be 40 days. The quality control department selects 15 bulbs for testing. The sampled bulbs last average of 280days with a standard deviation of 36 days. If the CEO\'s claim were true, what is the probability that 15 randomly selected bulbs would have an average life of no more than 290 days? 0.75 0.25 0.85 0.15

Solution

p ( x < 290)

p( z< 290 - 280 / 36/srqt(15))

p(z < 1.07) = 0.85