Question

What is the sum of the first fifteen multiples of 4? ​

Answer 1

Step-by-step explanation:

The multiples of 8 are 8,16,24,32…

These are in an A.P., having first term as 8 and common difference as 8.

Therefore, a=8,d=8, S

15

=?

S

n

=

2

n

[2a+(n−1)d]

S

15

=

2

15

[2(8)+(15−1)8]

=

2

15

[16+(14)(8)]

=

2

15×128

=960

Answer 2

Answer:

480

Step-by-step explanation:

4,8,12,....

here, a=4

d= 4

n= 15

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

S = 15/2[2*4+(15-1)*4]

S= 15/2(8+56)

S =15/2*64

S =15*32

S=480