Question 1 A study of data collected at a light bulb factory shows that a batch of 6000 light bulbs have a mean life of 1000 hours with a standard deviation of 75 hours. Assuming a Normal Distribution, estimate how many bulbs will fail before 900 hours.

Question 2 If x is normally distributed with u = 25 and s = 7 determine the probability that a randomly selected x lies between 18 and 32.

Question 3 Data collected from car dealers shows that oxygen sensors fitted to a popular model of car from a major manufacturer are failing on average at 40000km. with a standard deviation of 12000km. What is the probability that an oxygen sensor will fail before 30000km?

Question 4 In a driving school, the time taken by student drivers to complete a full circuit of the test course was found to be normally distributed with a mean of 50 minutes and a standard deviation of 15 minutes. What proportion of students will need an hour or more to complete the circuit?