Explanation : The series is 12 − 1, 22 − 1, 32 − 1 and so on. The next number is 92 − 1 = 80. Alternative solution: The differences between the numbers across the series are 3, 5, 7, 9, 11, 13, 15 and 17. The next number is 63 + 17 = 80.
Explanation : The series is 02 + 0, 12 + 1, 22 + 2, 32 +3 and so on. The missing number is 62 +6 = 42. The next number = 62 + 6 = 42. First alternative solution V The series is 0 × 1,1 × 2, ....... 1 × 2, 2 × 3, 3 × 4, 4 × 5 and 5 × 6 = 30. The next number is 6 × 7 = 42. Second alternative solution : The series is 12 − 1, 22 − 2, 32 − 3, 42 − 4, 52 − 5, 62 − 6, 72 − 7, 82 − 8 and so on.