Question

Find the sum of all 2digit natural number that are divisible by 5

Answer 1

Step-by-step explanation:

Hence, Sum of the numbers between 10 and 99 which is divisible by 5 is 945.

Answer 2

All two digit numbers divisible by 5 are 10, 15, 20,……85, 90, 95

Their sum = 10+15+20+25+…..+85+90+95

=5(2+3+4+5+6+…..+17+18+19)

=5{ (1+2+3+4+…….+17+18+19) - 1} (adding and subtracting 1)

=5{ (19) (20/2) - 1} (sum of first n natural numbers=n(n+1)/2)

=5(19×10–1)

=5×189

=945.

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