MathRevolution wrote:

[GMAT math practice question]

The formula for the sum of squares of integer between 1 and n is n(n+1)(2n+1) / 6 = 1^2 + 2^2 + … + n^2. The is the value of 11^2 + 12^2 + … + 20^2?

A. 2470

B. 2475

C. 2480

D. 2485

E. 2490

Sum of squares from 1 to 20 \(= \frac{20*21*41}{6} = 2870\) (use the formula given)

Sum of squares from 1 to 10 \(= \frac{10*11*21}{6} = 385\)

Hence sum of squares from 11 to 20 \(=\) Sum of squares from 1 to 20 \(-\) sum of squares from 1 to 10 \(= 2870-385 = 2485\)

Option

D