Question

Find the sum of first 20 multiples of 15

Answer 1

Answer:

a =15

d=15

n =20

Sn =n/2[2a+(n-1)d]

S20=10[30+(19)15]

S20=10[30+285]

S20=10*315

S20=3150

Answer 2

The sum of first 20 multiples of 15  is 3150

Step-by-step explanation:

The first 20 multiples of 15 are

15, 30, 45, 60,.....

This is an Arithmetic sequence since, the difference between two consecutive terms is equal.

Here, we have

a = 15

d = 30-15 = 15

n = 20

The sum of n term of an  arithmetic sequence is given by

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

Substituting the known values, we get

$S_n=\frac{20}{2}[2\cdot15+(20-1)15]\\\\S_n=10[30+19\cdot15]\\\\S_n=10\cdot315\\\\S_n=3150$

Therefore, the sum of first 20 multiples of 15  is 3150

#Learn More:

Find the sum of first 20 multiples of 7

https://brainly.in/question/1074550