Question

7. Find the sum of the first 15 multiples of 8​

Answer 1

The first 8 multiples of 8 are

8, 16, 24, 32, 40, 48, 56,64

These are in an A.P., having first term as 8 and common difference as 8.

Therefore, a = 8

d = 8

S15 = ?

Sn = n/2 [2a + (n - 1)d]

S15 = 15/2 [2(8) + (15 - 1)8]

= 15/2[6 + (14) (8)]

= 15/2[16 + 112]

= 15(128)/2

= 15 × 64

= 960

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Answer 2

Answer:

960...

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