M3.3.5 For the adult
Adding and taking away decimals
What is 2.5 + 0.75, and why must the decimal points line up?
What this chapter teaches
Decimals are added and taken away in columns, with the decimal points in a line so that tenths meet tenths. Multiplying by 10, 100 or 1 000 moves the digits left. Dividing moves them right. Rounding looks at the digit just after the place to keep.
Three questions to ask
There is no one right wording. Listen for the idea.
- Why must the decimal points line up when you add 3.4 and 0.27?
- What happens to the digits of 6.4 when you multiply by 100?
- Which whole number is 8.62 nearest to, and how can you tell?
After the chapter, the learner can
- Add and take away decimals by lining up the decimal points
- Multiply and divide decimals by 10, 100 and 1 000
- Round a decimal to the nearest whole or one decimal place
What they copy into their notebook
Line up the decimal points. Fill empty places with 0. × 10 moves digits left, ÷ 10 moves them right. To round, look at the next digit: 5 or more rounds up.