01Why this matters
Money and metric measurements use decimals constantly. Reading decimal places accurately prevents tenfold errors.
02See it
03Understand it
A decimal represents whole numbers and parts of a whole using places based on powers of ten.
The first place after the decimal point is tenths, then hundredths, then thousandths. The number 2.35 means 2 + 3/10 + 5/100. Trailing zeros do not change its value: 2.350 = 2.35. To add or subtract decimals, line up decimal points so that matching places are combined.
04Guided example
Add 2.35 m and 0.8 m.
- Write 0.8 as 0.80 so the hundredths columns line up.
- Add hundredths: 5 + 0 = 5. Add tenths: 3 + 8 = 11 tenths.
- Regroup 10 tenths as 1 whole: 2.35 + 0.80 = 3.15 m.
05Try it
06Practise it
07Use it in the real world
A $2.35 item and an $0.80 item total $3.15. Keeping two decimal places is useful for displaying money even when a trailing zero is not mathematically needed.
Go a little deeper
Multiplying by 100 changes the value by two places. In calculations, it is the digits’ place values that change; thinking of this avoids treating the decimal point as an object with its own value.
08Quick check
09Summary
A decimal represents whole numbers and parts of a whole using places based on powers of ten. Regroup 10 tenths as 1 whole: 2.35 + 0.80 = 3.15 m.
Before moving on, explain the worked example in your own words. Use the hint on any question you want to revisit.
10Key idea
0.01 = 1/100
Each decimal place to the right is one tenth of the previous place.
Decimal = numerator ÷ denominator
Find this in the formula library →