WAEC 2020 · Paper 1 · Q12

Sequences & series (AP, GP)

The first term of a geometric progression is 3 and the 5th term is 48. Find the common ratio.

Worked solution (try it first)

The 5th term of a G.P. is $ar^4$ , so $3r^4 = 48$ .
Divide by 3: $r^4 = 16$ .
Take the fourth root: $2^4 = 16$ , so $r = 2$ , option A.

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