Q21 of 26 Page 14

Calculate the standard deviation and mean diameter of the circles.

Classes

xi

yi = (xi – 42.5)/4

f i

f i y i

f i y i2

32.5-36.5

34.5

-2

15

-30

60

36.5-40.5

38.5

-1

17

-17

17

40.5-44.5

42.5

0

21

  0

  0

44.5-48.5

46.5

1

22

 22

 22

48.5-52.5

50.5

2

25

 50

100

Total

100  

 25

199

Mean diameter of the circles = = = 43.5

Variance (σ 2) = [(4)2/100][199 – 625/100] = 30.84
Hence the Standard Deviation is (σ ) = = 5.55

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