Q16 of 74 Page 9

Find the sum of all natural numbers between 100 and 1000 which are multiples of 5.


The next number to 100 which is multiple of 5 is 105. Similarly the next number to 105 multiple of 5 is 110. The greatest number multiple of 5 but less than 1000 is 995.

a = 105,

d = 110 – 105 = 5

an = a + (n - 1)d

995 = 105 + (n - 1)5

995 = 105 + 5n – 5

5n = 895

n = 179

Son =

      =

      = 98450

Therefore the sum of all natural numbers between 100 and 1000 are 98450.

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