Find the sum of all positive multiples of 5 less than 100.

Answer: Option C

Sum = 5 + 10 + 15 + 20 + .....+ 95 , It is an arithmetic progression
Number of terms (n)
= $$\frac{\text{Last term }-\text{ First term}}{\text{Differnce}}$$     + 1
⇒ n = $$\frac{95-5}{5}$$ + 1 = 19
So, sum = $$\frac{n}{2}$$ [2a + (n - 1)d]
Here, a = 5, n = 19, d = 5
Sum = $$\frac{19}{2}$$ [10 + (19 - 1)5]
        = 950