## Statistics- Ch. 2 Exercise 18 Ecommerce.com, a large Internet retailer

## Statistics- Ch. 2 Exercise 18 Ecommerce.com, a large Internet retailer

Ch. 2 Exercise 18

Ecommerce.com,

a large Internet retailer, is studying the lead time (elapsed time between

when an order is placed and when it is filled) for a sample of recent orders.

The lead times are reported in days.

Electricity

Cost Frequency

Middle

x-16.45

0 up to 5

6

3

-13.45

180.9025

1085.415

-1067.42

5 up to 10

7

7.5

-8.95

80.1025

560.7175

-508.218

10 up to 15

12

12.5

-3.95

15.6025

187.23

-37.23

15 up to 20

8

17.5

1.05

1.1025

8.82

131.18

20 up to 25

7

22.5

6.05

36.6025

256.2175

-98.7175

Total

40

63

-19.25

314.3125

2098.4

-1580.4

-39.51

a. How Many orders studied.

40

6.285698

mean =

[6*3+7*7.5+12*12.5+8*17.5+8*17.5+7*22.5)/(sum of the freqs) = 16.45

mean =

16.45

12.95

b.

What is the Midpoint of the first class (Round your answer to 1 decimal

place.)

c.

What are the coordinates of the first class for a frequency polygon assuming

we draw a frequency polygon using the midpoints? (Round your answer to 1

decimal place.)

x =

y =

6.29

Variance =

[ 6(3-12.95)^2 + 7(7.5-12.95)^2 + 12(12.5-12.95)^2 + 8(17.5-12.95)^2

+7(22.5-12.95)^2 ] / 40 =

=

40.21

Square root

6.341136

c. Use the

Empirical Rule to estimate the proportion of costs within two standard

deviations

of the

mean. What are these limits?

Lower =

-63.97

Upper =

56.66

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