Question

Mean marks of 40 students in a class is 15. If 20 students had got 2 marks more and the other 20 gets 1 mark less. Find the new mean.

Answer 1

the new mean will be 29

Answer 2

The new mean is 15.5

Solution:

The mean is given as:

$Mean = \frac{ \text { sum of all observations }}{ \text{ number of observations }}$

Mean marks of 40 students in a class is 15

Therefore,

$15 = \frac{ sum\ of\ all\ observations }{ 40}$

Sum of all observations = 15 x 40

Sum of all observations = 600

If 20 students had got 2 marks more and the other 20 gets 1 mark less

Therefore,

$New\ mean = \frac{ sum\ of\ all\ observations + 20(2) - 20(1) }{40}\\\\New\ mean = \frac{ 600 + 40 - 20 }{40}\\\\New\ mean = \frac{ 620}{40}\\\\New\ mean = 15.5$

Thus the new mean is 15.5

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