Decimals show parts of a whole.
In 12.5, the 5 means five tenths. In 8.75, the 7 means seven tenths and the 5 means five hundredths.
PRIMARY 5 · DECIMALS AND MEASUREMENT
The Garden Path Puzzle
Add and subtract decimal measurements without letting the decimal points wander away.
THE SITUATION
The path is nearly ready—but how long is it?
P5 pupils measure two sections of a new school-garden path. The first section is 12.5 m long and the second is 8.75 m. They must order enough edging for the whole path.
WHAT ARE WE TRYING TO SOLVE?Find the total length of the two path sections.
Decimal point under decimal point.
Write 12.50 above 8.75. Adding the zero does not change 12.5; it simply makes the place values easier to see.
12.50 + 8.75
Hundredths: 0 + 5 = 5
Tenths: 5 + 7 = 12; write 2 and carry 1.
Ones: 2 + 8 + 1 = 11.
Tens: 1 + 0 = 1.
Total path = 21.25 m
15-QUESTION PRACTICE
Help the garden team finish its measurements.
Begin with five warm-ups, apply the method in five situations, then finish with five reasoning challenges. Choose an answer and read the explanation—not only the tick.
1. A third path is made from 6.45 m and 3.8 m. What is its total length?
2. The team has 15 m of rope and uses 7.65 m. How much rope remains?
3. Two flower-bed edges measure 4.6 m and 2.35 m. What is their total length?
4. A 10 m plank is cut by 3.48 m. How much remains?
5. Three path pieces measure 7.25 m, 1.8 m and 0.95 m. What is the total?
GUIDED APPLICATION · 6–10
Now decide what each measurement means before calculating.
6. Which board is longer, 5.4 m or 5.04 m, and by how much?
7. Four equal edging pieces are each 2.75 m long. What is their combined length?
8. A 12.5 m strip loses a damaged 3.75 m section. How much usable strip remains?
9. A delivery route is 1.2 km long. How many metres is that?
10. A small stepping stone is 0.85 m wide. What is its width in centimetres?
REASONING CHALLENGE · 11–15
Show that your answer fits the situation.