WAEC 2021 · Paper 1 · Q5

Sequences & series (AP, GP)

Find the 5th term of the sequence $2, 5, 10, 17, \ldots$

Worked solution (try it first)

The gaps between terms are 3, 5 and 7, going up by 2 each time.
So the next gap is 9, and the 5th term is $17 + 9 = 26$ , option D.
Check with the rule $n^2 + 1$ : $5^2 + 1 = 26$ .

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