Question

Find the sum of whole number that are less than 100 and leave reminder 2 when divided by 5

Answer 1

Answer:

Well , the numbers which leaves remainder as 2 when divided by 5 are the ones with unit place as 7 or 2 {except 2 itself}.

So, below 100 it gives us-

(7+17+27+…+97)+(12+22+32+…+92)

I.e., we got two A.Ps.

Sum of any A.P is n/2(a+l) where,

n is total no of terms

a is the first term and

l is the last term.

So, 10/2(7+97) +9/2(12+92)

I.e., 5(104) + 9(52)

I.e., 520 + 468

I.e., 988