x, 9, 25, 48, 81, 121 find the value of x?
- 5
- 1
- 4
- 3
Explanation
- 9 - x = ?
- 25 - 9 = 16
- 48 - 25 = 23
- 81 - 48 = 33
- 121 - 81 = 40
Now look at the differences: 16, 23, 33, 40
Now check differences of differences:
- 23 - 16 = 7
- 33 - 23 = 10
- 40 - 33 = 7
There’s a slightly alternating pattern in second differences: 7, 10, 7...
Assuming this pattern continues backward, before 16, we should subtract 10 (alternating) ⇒ 16 - 10 = 6
So:
9 - x = 6 ⇒ x = 3
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