Question

Find the sum of the first 15 multiples of 8.
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Answer 1

Please refer to the attachment

Hope it helps u...✌

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Answer 2

Answer:

960

Step-by-step explanation:

They asked that sum of first 15 multiples of 8

First we should find multiples of 8

$8 \times 1=\red{8}$

$8 \times 2=\red{16}$

$8 \times 3=\red{24}$

$8 \times 4=\red{32}$

$8 \times 5=\red{40}$

$8 \times 6=\red{48}$

$8 \times7=\red{56}$

$8 \times 8=\red{64}$

$8 \times 9=\red{72}$

$8 \times 10=\red{80}$

$8 \times 11=\red{88}$

$8 \times 12=\red{96}$

$8 \times 13=\red{104}$

$8 \times 14=\red{112}$

$8 \times 15=\red{120}$

Now we should add the numbers of multiples of 8 of first 15

$8+16+24+32+40+48+56+64+72+80+88+96+104+112+120$

$= 960$

(or) we can do in another method

Let to be a is the first term and ‘d’ is the common difference and l is the last term of Given Arithmetic Sequence or Progression.

Arithmetic Sequence or Progression;- 8,16,24,32….

Here, the First term = 8

Common Difference = 8

Number of terms = 15

We know that Formula of Summation of Arithmetic Sequence or Progression.

$\boxed{Sn=n/2(2a+(n-1)d)}$  

S(15) = 15/2(2×8+(15-1)8

= 15/2(16+(14)8)

= 15/2(16+112)

= 15/2 x 128

= 15 x 64

= 960