The numbers from 1 to 100 which are divisible by 2 or 5 are 2, 4, 5, 6, 8, 10, 12, 14, 15, ....., 95, 96, 98, 100. ∴ Required sum = 2 + 4 + 5 + 6 + 8 + 10 + ..... + 95 + 96 + 98 + 100 = (2 + 4 + 6 + 8 + 10 + ..... + 96 + 98 + 100) + (5 + 15 + 25 + ...... + 95) = 2(1 + 2 + 3 + ...... + 50) + 5 (1 + 3 + 5 + ..... + 19) = 2 $\sum\limits_{k=1}^{50} k + 5n^2$ Since Sum of first n odd natural numbers is $n^2$ = 2 $\frac{50(50+1)}{2} + 5(10)^2$ = (50 × 51) + (5 × 100) = 2550 + 500 = 3050