WAEC 2020 · Paper 1 · Q13

Solve $\frac13(5 - 3x) < \frac25(3 - 7x)$ .

Worked solution (try it first)

Multiply both sides by 15, the LCM of 3 and 5: $5(5 - 3x) < 6(3 - 7x)$ .
Expand: $25 - 15x < 18 - 42x$ .
Add $42x$ and subtract 25 from both sides: $27x < -7$ .
Divide by 27, a positive number, so the sign stays: $x < -\frac{7}{27}$ , option D.