Find the sum of all two-digit numbers divisible by 5.

Explanation

Two-digit numbers divisible by 5: 10, 15, 20, …, 95. First term a = 10, last term l = 95, common difference d = 5. Number of terms n = (95 – 10)/5 + 1 = 18. Sum = (n/2)*(a + l) = 9 * (10 + 95) = 9 * 105 = 945.