Multiple choice general knowledge math & puzzles 21 24 30 33 39 ? 50 44 51 49 Reveal answer Fill a bubble to check yourself C Correct answer Explanation The pattern alternates between adding 3 and adding 6: 21+3=24, 24+6=30, 30+3=33, 33+6=39, 39+12=51. The addition doubles after each complete cycle (3,6 becomes 6,12). The next term is 51.