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An online pharmaceutical company obtained the following frequency distribution of shipping times (number of hours between the time an order is placed and the time the order is shipped) for a random sample of 40 orders. (Be sure to complete all appropriate columns and show your work).
Number of Hours fi
4 < 10 8
10 < 16 15
16 < 22 10
22 < 28 7
a. What is the approximate mean shipping time?
b. What is the approximate variance and standard deviation?


Sagot :

a) The approximate mean shipping time: X{bar} = 1.64

b) The approximate variance and standard deviation:

S² = 27.03, σ = 5.2

In this question, we have been given the frequency distribution of shipping times (number of hours between the time an order is placed and the time the order is shipped) for a random sample of 40 orders.

We need to find the approximate mean shipping time, variance and standard deviation.

Number of Hours        fi                midpoint

      4 < 10                  8                    7

     10 < 16                15                  13

     16 < 22                10                  19

     22 < 28                  7                   25

       SUM:                  40

a) the approximate mean shipping time:

X{bar} = (7.8 + 13.15 + 19.10 + 25.7)/40

X{bar} = 65.75/40

X{bar} = 1.64

b) the approximate variance:

S² = [(7.8 - 1.64)² + (13.15 - 1.64)²+(19.10 - 1.64)²+(25.7 - 1.64)²] / 39

S² = 1054.16/39

S² = 27.03

And the standard deviation:

σ = √S²

σ = √27.03

σ = 5.2

Therefore, for given frequency distribution,

a) mean = 1.64

b) variance = 27.03 and standard deviation = 5.2

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