Multiple choice Find the missing number in the series. (111, 91, 72, ?, 37) $54$ $55$ $21$ $43$ Reveal answer Fill a bubble to check yourself A Correct answer Explanation Find the pattern in differences: 111-91=20, 91-72=19. The difference decreases by 1 each time (20, 19, 18, 17). So: 72-18=54, and 54-17=37 (which matches the last term).