Given that the sum of the squares of the first seven natural numbers is 140, then their mean is :

Given,

N = 7

Sum of the squares of the first seven natural numbers = 140.

By formula,

Mean = $\frac{\text{Sum of observations}}{\text{Number of observations}}$

= $\frac{140}{7}$

= 20.

Hence, option 1 is the correct option.