Show your complete solutions and illustrate the shaded area on the normal curve.

1. A manufacturer of light bulbs produces bulbs that last a mean of 950 hours with a standard deviation of 120 hours. What is the probability that the mean lifetime a random sample of 10 of these bulbs is less than 900 hours?

2. The average public high school has 468 students with a standard deviation of 87. a. If a public school is selected, what is the probability that the number of students enrolled is greater than 400?

b. b. If a random sample of 38 public schools is selected, what is the probability that the number of students enrolled is between 445 and 485?

3. A population of 29-year old males has a mean salary of P29, 321 with a standard deviation of P2,120. If a sample of 100 men is taken, what is the probability that their mean salary will be less than P29,000?