🇨🇩 Measurement
⏱ 20 minOfficial programme: CD-P5-GRA-01
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In Tshikapa, Kavira fills a 20-litre container at the well and wonders how heavy it is. Her uncle measures his cassava field in ares. The bus to Kananga leaves at 7:50: how long will the journey last? In this lesson, you link litres, dm³ and kg for water, you convert land measures and you calculate with durations in hours and minutes.
Pure water: capacity, volume and mass
| Capacity | Volume | Mass of the water |
|---|---|---|
| 1 ml | 1 cm³ | 1 g |
| 1 l | 1 dm³ | 1 kg |
| 1 000 l | 1 m³ | 1 000 kg = 1 t |
These equalities are true for pure water. For oil or milk, one litre does not have the same mass.
Land measures. To measure fields and plots of land, we use:
Each unit is worth 100 times the next one. In the table, each column has two digits:
| ha | a | ca |
|---|---|---|
| 3 | 25 | 00 |
3.25 ha = 325 a = 32 500 ca = 32 500 m².
Mixed-unit quantities (durations). A duration such as 2 h 35 min is written with several units. Remember: 1 day = 24 h; 1 h = 60 min; 1 min = 60 s.
Adding: add each unit, then convert. 2 h 45 min + 1 h 30 min = 3 h 75 min = 4 h 15 min, because 75 min = 1 h 15 min.
Subtracting: if there are not enough minutes, borrow 1 h = 60 min. 5 h 10 min − 2 h 35 min = 4 h 70 min − 2 h 35 min = 2 h 35 min.
Kavira fills her container with 20 l of water. What is the volume of the water in dm³ and its mass in kg?
Step 1: 1 l = 1 dm³, so 20 l = 20 dm³.
Step 2: 1 l of water weighs 1 kg, so 20 l of water weigh 20 kg.
Answer: the water takes up 20 dm³ and weighs 20 kg (not counting the container).
A field measures 3 ha 25 a. Express its area in m². Then express 4 500 m² in ares.
Step 1: 3 ha = 3 × 10 000 m² = 30 000 m².
Step 2: 25 a = 25 × 100 m² = 2 500 m².
Step 3: 30 000 + 2 500 = 32 500 m².
Step 4: 4 500 m² ÷ 100 = 45 a.
Answer: 3 ha 25 a = 32 500 m² and 4 500 m² = 45 a.
The bus leaves Tshikapa at 7:50 and arrives in Kananga at 13:25. How long does the journey last?
Step 1: I set up 13 h 25 min − 7 h 50 min.
Step 2: 25 min is not enough to take away 50 min: I borrow 1 h. 13 h 25 min = 12 h 85 min.
Step 3: 85 min − 50 min = 35 min; 12 h − 7 h = 5 h.
Answer: the journey lasts 5 h 35 min.
Watch out: an hour has 60 minutes, not 100. So 1.5 h = 1 h 30 min, not 1 h 50 min. When you add durations, change each group of 60 min into 1 h.
Another trap: the centiare is 1 m², not 1 cm².
Answer one exercise at a time. Your answer is checked right away, with an explanation.
Exercise 1 of 9
★ EasyConvert 7 ha into ares.
