Mathematics

Find the sum of the first 15 multiples of 8.

AP

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Answer

List of multiples of 8 are :

8, 16, 24, 32, ……..

The above list is an A.P. with first term (a) = 8 and common difference (d) = 16 - 8 = 8.

By formula,

Sum of first n terms = S_n = $\dfrac{n}{2}[2a + (n - 1)d]$

Substituting values we get :

$S_{15} = \dfrac{15}{2}[2 \times 8 + (15 - 1) \times 8] \\[1em] = \dfrac{15}{2}[16 + 14 \times 8] \\[1em] = \dfrac{15}{2} \times [16 + 112] \\[1em] = \dfrac{15}{2} \times 128 \\[1em] = 15 \times 64 \\[1em] = 960.$

Hence, sum of first 15 multiples of 8 = 960.

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Mathematics

Find the sum of the first 15 multiples of 8.

AP

Answer

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