The sum of all natural numbers lying between 100 and 1000 which are multiple of 5 is

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Professor PC Thomas Classes · Answer

The sequence is $105, 110, \ldots, 995$. Number of terms $n = \frac{995 - 105}{5} + 1 = 179$. Sum = $\frac{179}{2}(105 + 995) = \frac{179}{2}(1100) = 98450$.