Question

the sum of all 2-digit numbers divisible by 5 is

Answer 1

Required numbers are 10,15,20,25,...,95

This is an A.P. in which a=10,d=5 and l=95.

Let the number of terms in it be n.Then t=95

So a+(n-1)d=95.

10+(n-1)*5=95,then n=18.

Required sum=n/2(a+l)=18/2(10+95)=945.

Answer 2

Required numbers are 10,15,20,25,...,95

This is an A.P. in which a=10,d=5 and l=95.

Let the number of terms in it be n.Then t=95

So a+(n-1)d=95.

10+(n-1)*5=95,then n=18.

Required sum=n/2(a+l)=18/2(10+95)=945.