JAMB 1994 · UME · Q1

Evaluate $\frac13 \div \left[\frac57\left(\frac{9}{10} - 1 + \frac34\right)\right]$ .

Worked solution (try it first)

Inside the bracket, use the LCD 20: $\frac{9}{10} - 1 + \frac34 = \frac{18 - 20 + 15}{20}$
$= \frac{13}{20}$ .
Multiply by $\frac57$ : $\frac57 \times \frac{13}{20} = \frac{13}{28}$ .
To divide, multiply by the reciprocal: $\frac13 \times \frac{28}{13} = \frac{28}{39}$ , option A.