Problem Solving (PS) | The incomplete table above shows a distribution of scores for a class

Responding to a pm: Use deviations from mean approach for quick calculations.

Mean is 78.
83 is 5 in excess so we have 5*5 = 25 excess (because 83 appears 5 times)
70 has 8 deficit from 78 and appears 6 times so 48 deficit
92 has 14 excess and appears 3 times so 42 excess.
64 has 14 deficit.
Currently excess is 67 and deficit is 62. So we need another 5 deficit to make them equal. Since the unknown number appears 5 times, it must have a deficit of 1 i.e. the number must be 77.

Answer (C)

The following video on Arithmetic Mean will help:

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Statistics : Posted by KarishmaB • on 15 Oct 2018, 11:07 • Replies 7 • Views 8077

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