1. Problem: The mass of a child increases from 12.0 kg to 16.2 kg. Work out the percentage increase. 2. Formula: Percentage increase = $$\frac{\text{New value} - \text{Original value}}{\text{Original value}} \times 100$$ 3. Calculation: $$\frac{16.2 - 12.0}{12.0} \times 100 = \frac{4.2}{12.0} \times 100$$ 4. Simplify fraction: $$\frac{\cancel{4.2}}{\cancel{12.0}} = 0.35$$ 5. Multiply by 100: $$0.35 \times 100 = 35$$ 6. Answer: The percentage increase is **35%**.