Question

Best Electronics offers a “no hassle” returns policy. The number of items returned per day follows the normal distribution. The mean number of customer returns is 8.4 per day and the standard deviation is 1.70 per day. Refer to the table in Appendix B.1.  

a. In what percentage of the days 7 or fewer customers returning items? (Round z-score computation to 2 decimal places and the final answer to 2 decimal places.)

Percentage            %

b. In what percentage of the days between 12 and 15 customers returning items? (Round z-score computation to 2 decimal places and the final answer to 2 decimal places.)

Percentage            %

c. Is there any chance of a day with no returns?

Answer 1

The mean number of customer returns i.e =8.4
per day and the standard deviation = 2.25 per day

let x is the number of items returned per day follows the normal distribution.

ie z =

ans a) P ( x<- 7) =P{z <_ (7-8.4) /2.25)}

P ( x<- 7) = P{z <_ -0.62} = .2676 = 26.76%

26.76%  percentage of the days 7 or fewer customers returning items.

ans b)  P (12<- x<- 15) = P()

  P (12<- x<- 15) = = 0.0531 =5.31 %

5.31%  percentage of the days between 12 and 15 customers returning items

ans c )   P ( x<- 0) =

P ( x<- 0) = = 0.000099999999999988