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## 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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