Question

The mean of 10 numbers is 15 and that of another 20 number is 24 then the mean of all 30 observations is

Answer 1

sum of 10 numbers= 10×15= 150
sum of 20 numbers= 20×24= 480
sum of 30 numbers= 150 +480= 630
mean of 30 numbers= 630÷30= 21

Answer 2

Mean of all 30 observations\numbers is 21.

Given:

• The mean of 10 numbers is 15.
• And that of another 20 number is 24.

To find:

• The mean of all 30 observations.

Solution:

Formula to be used:

$\bf Mean=\frac{\Sigma x_i}{n}$

here

$\Sigma x_i$: sum of all observations.

n: Total number of observation.

Step 1:

Find sum of 10 observations.

here,

Mean= 15

n= 10

Sum of 10 observations= 15×10

Sum of 10 observations= 150.

Step 2:

Find sum of 20 observations.

here,

Mean= 24

n= 20

Sum of 20 observations= 24×20

Sum of 20 observations= 480

Step 3:

Find sum of all 30 observations/numbers.

Sum of 30 observations=150+480

Sum of 30 observations=630

Step 4:

Find mean of all 30 observations.

$\Sigma x_i = 630$

n=30

$Mean = \frac{630}{30}$

or

$\bf Mean = 21$

Thus,

Mean of all 30 numbers is 21.

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