Assume the relevant data follows normal distribution. A brand of smart phone has an estimated mean life span of 4 years. The standard deviation is 1.5 year. The factory produces 50,000 such phones. Estimate how many of them will have a life span between 3 and 5 years.

The mean mark on a final exam was 76 and the standard deviation was 4. The bottom 30 % of the students are to receive a failing grade. What is the minimum mark a student must get in order to pass? Assume the marks obey normal distribution.