JAMB 1987 · UME · Q30

Sequences & series (AP, GP)

Find the eleventh term of the progression $4, 8, 16, \dots$

Worked solution (try it first)

This is a G.P. with $a = 4$ and $r = 8 \div 4 = 2$ .
The $n$ th term is $ar^{n - 1}$ , so the eleventh term is $4 \times 2^{10}$ .
Write 4 as $2^2$ and add the powers: $2^2 \times 2^{10} = 2^{12}$ , option B.

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