1. **State the problem:** Madhu bought a coat costing 1800 before tax and paid 1980 after including VAT. We need to find the rate of tax charged. 2. **Identify given values:** - Cost price before tax = 1800 - Cost price after tax = 1980 3. **Calculate the amount of tax paid:** $$\text{Tax amount} = 1980 - 1800 = 180$$ 4. **Calculate the rate of tax:** The rate of tax is the tax amount divided by the original price, multiplied by 100 to get a percentage. $$\text{Rate of tax} = \frac{180}{1800} \times 100 = 10\%$$ 5. **Final answer:** The rate of tax charged is 10%.