Question

FIND THE SUM OF FIRST 20 MULTIPLE OF 9​

Answer 1

Here,

let form an AP,

where a=9, d=9 and n=20

So,

AP:- 9,18,27,36,45......

Now,

Sum of values up to 20 terms = n/2 [a×2 + (n-1)d]

=> (20/2) [9×2 + (20-1)9]

=> (10)×(18 + 171)

=> (10)×(189)

=> 1890

So, the sum of first of 20 multiples of 9 is 1890.

Answer 2

let form an AP

where a=9, d=9 and n=20

So,

AP:- 9,18,27,36,45...

Now,

Sum of values up to 20 terms = n/2 [a×2 + (n-1)d]

=> (20/2) [9×2 + (20-1)9]

=> (10)×(18 + 171)

=> (10)×(189)

=> 1890

So, the sum of first of 20 multiples of 9 is 1890.