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If for somex in R, the frequency distrib...

If for some`x in R`, the frequency distribution of the marks obtained by 20 students in a test is:
Then the mean of the marks is:

A

3.2

B

2.8

C

3

D

2.5

Text Solution

Verified by Experts

The correct Answer is:
B
Total number of students are 20
So, `(x+1)^(2)+(2x-5)+(x^(2)-3x)+x=20`
`x^(2) + 2x +1 +2x -5 + x^(2) -3x +x=20`
`2x^(2) + 2x - 24=0`
`x^(2) + x-12=0`
`x=-4, x=3`
But x is positive so, x=3
Now average marks (mean of the marks) `=(16 xx 2+1 xx 3+0 xx 5 + 7 xx 3)/20 = 56/20=2.8`
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