JAMB 2004 · UME · Q18

The $n$ th terms of two sequences are $Q_n = 3 \cdot 2^{n - 2}$ and $U_m = 3 \cdot 2^{2m - 3}$ . Find the product of $Q_2$ and $U_2$ .

Worked solution (try it first)

Put $n = 2$ into $Q_n$ : $Q_2 = 3 \times 2^0 = 3$ .
Put $m = 2$ into $U_m$ : the power is $2 \times 2 - 3 = 1$ , so $U_2 = 3 \times 2 = 6$ .
So $Q_2 \times U_2 = 3 \times 6 = 18$ , option D.