Multiple choice general knowledge math & puzzles What is the sum of 5 and 15 75 70 20 10 Reveal answer Fill a bubble to check yourself C Correct answer Explanation The sum of 5 and 15 is 20. This is a basic arithmetic operation. 75 and 70 are results of multiplication (5x15 and 5+15 treated incorrectly), while 10 is the difference, not the sum.