[8215] The sum of the squares of the first 15 positive integers is equal to 1240. What is the sum of the sq

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The sum of the squares of the first 15 positive integers is equal to 1240. What is the sum of the squares of the second 15 positive integers?

2480

3490

6785

8215

Explanation:

Sum of square of n numbers is found using the formula $\dfrac{n × (n + 1) (2n + 1)}{6}$
Sum of 1st 15 numbers = 1240
Sum of squares from 16 to 30 = Sum of squares of 1st 30 +ve integers - Sum of squares of 1st 15 +ve integers.
= $\dfrac{30 × 31 × 61}{6}$ - 1240
= 9455 – 1240
= 8215

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