Find the sum of first 15 multiples of 8.

1.	Find the sum of first 15 multiples of 8.
Answer» The first 15 multiples of 8 are 8, 16, 24, 32,……. This is an AP in which a = 8, d = (16 - 8) = 8 and n = 15. Thus, we have: l = a + (n - 1)d = 8 + (15 - 1)8 = 120 ∴ Required sum = \(\frac{n}{2}(a+l)\) = \(\frac{15}{2}[8+120]=15\times64=960\) Hence, the required sum is 960.

Answer»

The first 15 multiples of 8 are 8, 16, 24, 32,…….

This is an AP in which a = 8, d = (16 - 8) = 8 and n = 15.

Thus, we have:

l = a + (n - 1)d

= 8 + (15 - 1)8

= 120

∴ Required sum = \(\frac{n}{2}(a+l)\)

= \(\frac{15}{2}[8+120]=15\times64=960\)

Hence, the required sum is 960.

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