Question

To find the average of first 21 multiples of 9

Answer 1

Answer:

(n+1)/2

Therefore 20*21/2

210/2the mean of this is 10.5

Answer 2

Answer:

the average of first 21 multiples of 9 is 99.

Step-by-step explanation:

we have to find the average of first 21 multiples of 9

The first 21 multiples of 9 are:

9, 18, 27 ,36 ,45 ,54 ,63 ,72 ,81 ,90 ,99 ,108 ,117 ,126 ,135 ,144 ,153 ,162 ,171 ,180 ,189

Calculate the average by $A =\frac{\text{sum of all number}}{\text{total numbers of terms}}$

$A =\frac{2079}{21}$

$A =99$

Hence, the average of first 21 multiples of 9 is 99.