Question

The GMAC Insurance company reported that the mean score on the National Drivers Test was 72.0 with a standard deviation of 3.3 points. The test scores are approximately bell-shaped. Approximately 68% of all test scores were between two values A and B. What is the value of A? Write only a number as your answer. Round to one decimal place. Your Answer: Answer Question 10 (1.2 points) In a large sample of customer accounts, a utility company determined that the average number of days between when a bill was sent out and when the payment was made is 20 with a standard deviation of 13 days. Assume the data to be approximately bell-shaped. Approximately 95% of all customer accounts have the average number of days between two values A and B. What is the value of B? Write only a number as your answer.

Answer 1

1)

Bell shaped data means normally distribution

According to the emperical rule

If the data is normally distributed

Then 68% lies in between mean - s.d and mean + s.d

95% lies in between mean - 2*s.d and mean + 2*s.d

99.7% lies in between mean - 3*s.d and mean + 3*s.d

Mean = 72

S.d = 3.3

So, 68% lies in between 72 - 3.3 and 72 + 3.3

So A = 72 - 3.3

= 68.7

10)

95% lies in between mean - (2*s.d) and mean + (2*s.d)

B = 20 + (13*2) = 46