Difficulty: Easy
Correct Answer: 35
Explanation:
First differences
15 − 3 = 12
(?) − 15 = 20
63 − (?) = 28
99 − 63 = 36
143 − 99 = 44
Pattern
Differences increase by 8: 12, 20, 28, 36, 44, …
Compute
15 + 20 = 35; then 35 + 28 = 63, matching the series.
Discussion & Comments