Question

Maths 10 class,find the sum of all the 2-digit numbers divisible by 3

Answer 1

The AP is 12,15, 18....,99

first term=12

d=3

an =99

a+(n-1)d=99

12+(n-1)3=99

(n-1)3=87

(n-1)=29

n=30

sum=n/2(a+l)

=30/2(12+99)

=15*111

=1665