Multiple choice general knowledge math & puzzles Look at this series: 80, 10, 70, 15, 60, ... What number should come next? 20 25 30 50 Reveal answer Fill a bubble to check yourself A Correct answer Explanation This series consists of two alternating patterns. The first pattern (80, 70, 60) subtracts 10 each time. The second pattern (10, 15, ...) adds 5 each time. Following the second pattern, 15 + 5 equals 20.