Question

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

Answer 1

Answer:

960

Step-by-step explanation:

first 15 multiples of 8 means 8,16,24,32,....120.

The above series is in Arthimetic progression with common difference 8.

so the sum of 1st 15 terms is,

S15 = n/2(a+l),

= 15/2*(8+120),

= 15*64,

= 960.

Answer 2

Answer:

960

Step-by-step explanation:

Multiples of 8 : 8,16,24....

a = 8 , d = 8 and n = 15

Sₙ = n/2 [ 2a + ( n-1 ) d ]

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

Sₙ = 15/2 [ 16 + 112 ]

Sₙ = 15/2 × 128

Sₙ = 15 × 64

Sₙ = 960