Question

18) Find the sum of first 15 positive integers divisible by 6​

Answer 1

the AP is 6,12,18...

a=6

d=6

n=15

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

=7.5[12+14*6]

=720

Answer 2

Answer:

720 is answer

Step-by-step explanation:

Ap:6 ,12, 18, 24,...........90

Sn=n/2 × (2a+(n-1)d)

Here

a=6

d =6

n=15

So

Sn= 15/2 × (2×6 + (15-1)6)

Sn= 15 (6+ 42)

Sn = 15 × 48

Sn= 720

• Alternative Method

Sn= n/2 × (a + l)

Sn = 15/2 × (6+90)

Sn = 15/2 × 96

Sn= 15 × 48

Sn= 720