1. The mean number of hours a student spends on social media is 4.5 hours per weekend. Assuming the standard deviation is 1.5, find the probability of spending:

I. Between 1.5 and 3 hours.

II. More than 5 hours.

2. The incomes of junior staff in a large petrochemical company are normally distributed with a standard deviation of SAR 500. A cutback is pending, at which time those who earn less than SAR 1000 will be discharged. If such a cut represents 8 % of the junior staff, what is the current mean salary of the junior staff group?

3. The time it takes to complete an online assignment is approximately normally distributed with a mean of 40 minutes and a standard deviation of 6.45 minutes. An instructor would like to claim that 93.7% of the students completed the assignment within c minutes. Find the value of c which makes this statement true.

4. The weight of watermelons sold at Danube are normally distributed with a standard deviation of 2.8 lb. Find the mean weight of Danube's watermelons if only 3 % weigh less than 15 lb.

5. For a particular age group of adult males, the distribution of cholesterol readings, in mg/dl, is normally distributed with a mean of 210 and a standard deviation of 15.

a) What percentage of this population would have readings exceeding 250?

b) What percentage would have readings less than 150?