Question

18) A distribution of random numbers has a mean or 10 and a standard deviation of 1. The probability of a score below 9 is.

A. 16%

B.  84%

19) A distribution of random numbers has a mean or 10 and a standard deviation of 1. The probability of a score above 11 is

A. 16%

B. 33%

20) The vice president of marketing wants to issue a press release anytime monthly sales at on the top 5% for all months. Average sales for a month is $100M and the standard deviation of monthly sales is $10M. At what level of sales should the vice president issue the press release?

A. $ 16.5M

B. $116.5M

Answer 1

For all the problems I have used Normal distribution

18.

Let   

So P(X<9)=  

where so answer is 15.87% 16%

19.

Let

So, P(X>11)=P(Z>1)=1-P(Z<=1)=1-0.8413 1-0.84=0.16 so answer is 16%

20.

since we need op 5% so we consider the probability 0.95

So,

implies implies

using standard normal table we get =1.65 so x=116.5 answer 116.5M