Question

Find the sum of the first 30 multiples of 8.

Answer 1

Step-by-step explanation:

sum of the arithmetic sequence

a1 = 8

a2 = a1 + 8 = 8+8 = 16

...

an = 8×n

the sum of the first n elements of such a series is

n/2 × (2×a1 + (n - 1)×d]

with d being the difference between 2 consecutive elements (= the added constant).

so,

s30 = 30/2 × (2×8 + 29×8) = 15×(31×8) = 3720