3. An electrical company claims that the average life of the bulbs it manufactures is 1200 hours with standard deviation of 250 hours. If a random sample of 100 bulbs is chosen, what is the probability that the sample mean will be: a. Greater than 1150 hours? b. Less than 1250 hours? C. Between 1100 and 1300 hours? 4. A manufacturer receives a shipment of 500 spare parts from a supplier who claims that the lengths of the spare parts are approximately normally distributed having a mean of 2.5 cm and standard deviation of 0.04 cm. If the manufacturer takes a 10% random sample from the shipment, what is the probability that he gets a mean length of: a. More than 2.22 cm? b. More than 2.40 cm? c. Between 1.80 cm and 2.40 cm