Find the greatest value of (a +
b) such that an 8-digit number 4523a60b is divisible by 15.

Factors of 15 = (3 × 5) and the divisibility rule of 15 says that sum of digits be divided by 3 and the last number will be 5. Possible values of b are 0 and 5 Now, 4 + 5 + 2 + 3 + a + 6 + 0 + 0 = 20 + a Here a can be 1, 4, 7 For greatest we need to take 7 So, a + b = 7 + 0 = 7 which is not present in the option Again, 4 + 5 + 2 + 3 + a + 6 + 0 + 5 = 25 + a Here a can be 2, 5, 8 For greatest we need to take 8 So, a + b = 8 + 5 = 13  which is present in the option ∴ Required answer is 13