Question

What is the sum of the first 15 multiples of 9?

Answer 1

Answer:

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 

Step-by-step explanation:

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Answer 2

Answer:

9, 18, 27, 36, ,45, 63,72,81,90,99,,108,117,126,135,144; these are the multiple s of 9, and the sum = 1170

Step-by-step explanation:

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