Another Peek Beyond the Point

Overview

Building on decimals, this chapter covers operations with decimals: addition, subtraction, multiplication and division, along with practical uses like money and measurement.

Key concepts

• Line up decimal points before adding or subtracting.
• Multiplying decimals: count decimal places in the answer.
• Dividing decimals using equivalent whole-number division.
• Using decimals in money, length and weight.

Important formulae

• Number of decimal places in a product = sum of decimal places of factors
• To divide by 10, 100, ... shift the point left
• To multiply by 10, 100, ... shift the point right

Solved example

1. Multiply 0.3 × 0.4.
2. Multiply as whole numbers: 3 × 4 = 12.
3. Total decimal places = 1 + 1 = 2, so answer = 0.12.

Important questions

1. Add 12.5 + 3.75.
2. Subtract 9.6 − 4.85.
3. Find 2.5 × 4.
4. Divide 6.4 ÷ 8.

Quick revision

Align points for + and −. For ×, multiply normally then place the point by counting decimal places. Shifting the point handles multiplying or dividing by powers of 10.