Question

Find the sum of all natural number between 100to500 which are divisible by 7

Answer 1

a=105

d=7

l=497

l=a+(n-1)d

497= 105+ (n-1) 7

392= (n-1)7

56=(n-1)

57=n

Sum=n/2(2a+(n-1)d)

=57/2(2×105+ 56×7)

=57/2(210+392)

Answer 2

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