The average of first 6 positive multiples of 6 will be __________.

Correct option is C

Given:
Average of first 6 positive multiples of 6
Formula Used:
​$$\text{Average} = \frac{\text{Sum of observations}}{\text{Number of observations}}$$​​
Solution:
First 6 positive multiple of 6 are 6, 12, 18, 24, 30, 36
Required average = $$\frac{6 + 12 + 18 + 24 + 30 + 36}{6} = \frac{126}{6} = 21$$​​
∴ The required average is 21.