An algebra problem by arko roychoudhury

Algebra Level 2

Obtain the sum of all positive integers up to 1000, which are divisible by 5 and not divisible by 2.

40000 90000 45000 50000 9 54000 76575 74634

Arko Roychoudhury by arko roychoudhury , 20, India

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3 solutions

The numbers that have to be summed are 5,15,25,35... This is a progression with formula u(n) = 10n +5. The sum of this progression is: 0.5 x (n+1) x (10n +5 +5). Since 995 is the last to be summed n is 99. So we get 0.5 x 100 x 1000 = 50,000.

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Edwin Gray
Jul 8, 2018

We have an arithmetic progression with 100 terms first term = 5, last term = 995, so S = (n/2) (a + l) = 50 1000 = 50,000. ED Gray

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Ramiel To-ong
Aug 29, 2017

NICE PROBLEM

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