1. **Problem Statement:** Multiply decimals mentally by 0.1, 0.01, and 0.001. 2. **Key Concept:** Multiplying a decimal by 0.1, 0.01, or 0.001 shifts the decimal point to the left by 1, 2, or 3 places respectively. 3. **Rules:** - Multiplying by 0.1 moves the decimal point 1 place left. - Multiplying by 0.01 moves the decimal point 2 places left. - Multiplying by 0.001 moves the decimal point 3 places left. 4. **Example from Exercise Set A:** - For 0.2 x 0.1: Move decimal 1 place left: $0.2 \times 0.1 = 0.02$ - For 0.458 x 0.1: $0.458 \times 0.1 = 0.0458$ - For 0.963 x 0.01: Move decimal 2 places left: $0.963 \times 0.01 = 0.00963$ 5. **Calculations for Exercise Set A (first 3 problems):** 1. $0.2 \times 0.1 = 0.02$ 2. $0.458 \times 0.1 = 0.0458$ 3. $0.963 \times 0.01 = 0.00963$ 6. **Explanation:** Each multiplication shifts the decimal point left by the number of zeros in the multiplier after the decimal. 7. **Final answers for the first problem set (first 3 problems):** - 0.02 - 0.0458 - 0.00963 This method applies similarly to all other problems in the sets.