 # RS Aggarwal Solutions Class 9 Mathematics Solutions for Mean Median And Mode Of Ungrouped Data Exercise 18B in Chapter 18 - Mean Median And Mode Of Ungrouped Data

Question 9 Mean Median And Mode Of Ungrouped Data Exercise 18B

Find the missing frequency p for the following frequency distribution whose mean is 28.25.

x f
15 8
20 7
25 p
30 14
35 15
40 6

x f xifi
15 8 120
20 7 140
25 p 25p
30 14 420
35 15 525
40 6 240
Σ fi = 50 + p Σ fi xi = 1445 + 25p

It is given that

Mean = 28.25

We know that

Mean = Σ fi xi/ Σ fi

So we get

(1445 + 25p)/ (50 + p) = 28.25

On further calculation

1445 + 25p = 1412.50 + 28.25p

So we get

-28.25p + 25p = -1445 + 1412.50

It can be written as

-3.25p = -32.5

By division

p = 10

Therefore, the value of p is 10.

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