Question

Sum of all positive integers 1 to 1000 which is divisible by 5

Answer 1

The reqd. A.P is

5, 10, 15, 20.......1000

Let,

Tn=1000

a+(n-1)d=1000

5+(n-1)5=1000

(n-1)5=1000-5

n-1=995/5

n=199+1

n=200

Sn=200/2(5+1000)

=100×1005

=100500, which is the reqd. value

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