JAMB 2003 · UME · Q3

Simplify $213_4 \times 23_4$ .

Worked solution (try it first)

Change to base ten: $213_4 = 32 + 4 + 3 = 39$ and $23_4 = 8 + 3 = 11$ .
Multiply: $39 \times 11 = 429$ .
Change back: $429 = 1 \times 256 + 2 \times 64 + 2 \times 16 + 3 \times 4 + 1$ , so the answer is $12231_4$ , option D.