JAMB 1986 · UME · Q1

Evaluate $212_3 - 121_3 + 222_3$ .

Worked solution (try it first)

Change to base ten: $212_3 = 18 + 3 + 2 = 23$ , $121_3 = 9 + 6 + 1 = 16$ and $222_3 = 18 + 6 + 2 = 26$ .
Work it out: $23 - 16 + 26 = 33$ .
Change back: $33 = 27 + 6$
$= 1 \times 27 + 0 \times 9 + 2 \times 3 + 0$ , so the answer is $1020_3$ , option C.