Question

find the sum of 80 multiple of 3

Answer 1

Answer:

9720

Step-by-step explanation:

Multiples of 3 are

3, 6, 9, 12, 15, .....upto 80 terms,  which forms an AP where

First term (a) = 3

Common difference ( d ) = 3

number of terms ( n ) = 80

We know that Sum of n terms is

$\frac{n}{2}[2a+(n-1)d]$

Putting values n = 80, a = 3, d = 3

$\frac{80}{2}[2 \times 3+(80-1)\times 3]$

 = 40 (6 + 237)

 = 40 × 243

 = 9720

Hence, sum of first 80 multiples of 3 = 9720