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

Question 5 Mean Median And Mode Of Ungrouped Data Exercise 18A

If the mean of five observations x, x + 2, x + 4, x + 6, x + 8 is 13, find the value of x and hence find the

mean of the last three observations.

We know that

Number of observations = 5

It is given that mean = 13

We can write it as

[x + (x + 2) + (x + 4) + (x + 6) + (x + 8)]/5 = 13

On further calculation

5x + 20 = 13 (5)

So we get

5x + 20 = 65

By subtraction

5x = 45

By division

x = 9

By substituting the value of x

We know that the last three observations are

9 + 4 = 13

9 + 6 = 15

9 + 8 = 17

We know that

Mean of last three observations = (13 + 15 + 17)/3

On further calculation

Mean of last three observations = 45/3

By division

Mean of last three observations = 15

Therefore, the mean of last three observations is 15.

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