JAMB 2002 · UME · Q3

Evaluate $\dfrac{0.21 \times 0.072 \times 0.0054}{0.006 \times 1.68 \times 0.063}$ correct to four significant figures.

Worked solution (try it first)

Cancel before multiplying: $\frac{0.21}{0.063} = \frac{10}{3}$ , $\frac{0.072}{1.68} = \frac{3}{70}$ and $\frac{0.0054}{0.006} = 0.9$ .
Multiply: $\frac{10}{3} \times \frac{3}{70} = \frac17$ , and $\frac17 \times 0.9 = \frac{9}{70}$ .
$\frac{9}{70} = 0.128571\ldots$ .
The fifth significant figure is 7, so round up: 0.1286, option A.