Question

Find the sum of all 2 digit natural numbers which
are divisible by 3 and 4.​

Answer 1

Answer:

1665

First two digit number divisible by 3 = 12

Last two digit number divisible by 3 = 99

∴ First term, (a)=12

Common difference, (d)=3

Last term, (l)=99

n=?

As we know that,

an=a+(n−1)d

∴99=12+(n−1)3

⇒(n−1)

387⇒n=29+1=30

∴ Sum of n terms of an A.P., when last term is known is given by-

Sn=2n(a+l)

∴S30= 230(12+99)

⇒S 30 =15×111=1665