1. **Problem:** If the price of petrol is increased by 10% and then decreased by 10%, what is the equivalent change in percentage? 2. **Formula:** When a quantity is increased by $p\%$ and then decreased by $q\%$, the net change is given by: $$\text{Net change} = \left(1 + \frac{p}{100}\right) \times \left(1 - \frac{q}{100}\right) - 1$$ 3. **Step-by-step solution:** - Initial price = $P$ - After 10% increase, new price = $P \times \left(1 + \frac{10}{100}\right) = P \times 1.1$ - After 10% decrease on new price, final price = $P \times 1.1 \times \left(1 - \frac{10}{100}\right) = P \times 1.1 \times 0.9 = P \times 0.99$ 4. **Interpretation:** - The final price is $0.99P$, which is 99% of the original price. - This means the price decreased by $1\%$ overall. 5. **Answer:** The equivalent change is a 1% decrease. **Final answer:** c) 1% decreased