Question

The sum of ${15}^2+{16}^2+{17}^2+.....+{30}^2$ is equal to:

• A. 8840
• B. 8440
• C. 8540
• D. 8450
• E. 8000

Answer 1

Answer: (B)

${15}^2+{16}^2+{17}^2......+{30}^2$ $=1^2+2^2+...+{30}^2-(1^2+2^2+....+{14}^2)$
$=\frac{30(31)(61)}{6}-\frac{14(15)(29)}{6}$
$=\frac{56730-6090}{6}=8440$