Capacity Measurements
Primary 4 · Mathematics
Capacity Measurements
Lesson 3 of 4
20 min
Let's begin
Mutesi's family has a water tank behind the house. On Monday it holds 450 L. On Tuesday it rains, and 275 L more runs in from the roof.
Then the family uses water for cooking, washing and the cow. How much is in the tank now? How much is left after they use some?
Today you will add and take away capacities, with whole numbers and with decimals.
You can only add or subtract amounts in the same unit. If one amount is in L and the other is in mL, change one of them first.
Worked example 1
450 L + 275 L
Step 1 Add the ones: 0 + 5 = 5.
Step 2 Add the tens: 5 + 7 = 12 tens. Write 2, carry 1 hundred.
Step 3 Add the hundreds: 4 + 2 + 1 = 7.
So the tank now holds 725 L.
Worked example 2
2 L 750 mL + 1 L 500 mL
Step 1 Add the mL: 750 + 500 = 1 250 mL.
Step 2 1 250 mL is 1 L and 250 mL. Keep 250 mL and carry 1 L.
Step 3 Add the litres: 2 + 1 + 1 = 4 L.
The answer is 4 L 250 mL.
Worked example 3
5 L 200 mL − 2 L 600 mL
Step 1 200 mL take away 600 mL? Not enough! Borrow 1 L from the 5 L. 1 L = 1 000 mL, so now you have 1 000 + 200 = 1 200 mL, and 4 L.
Step 2 Subtract the mL: 1 200 − 600 = 600 mL.
Step 3 Subtract the litres: 4 − 2 = 2 L.
The answer is 2 L 600 mL. Check by adding: 2 L 600 mL + 2 L 600 mL = 4 L 1 200 mL = 5 L 200 mL. It works!
Worked example 4
A full jerrycan holds 20 L. Uwase pours out 7.35 L. How much is left?
Step 1 Write 20 as 20.00, so it has two decimal places like 7.35.
Step 2 Line up the decimal points, one under the other.
Step 3 Subtract as usual: 20.00 − 7.35 = 12.65. So 12.65 L is left.
Worked example 5
3.4 L + 1.25 L. Write 3.4 as 3.40. Then 3.40 + 1.25 = 4.65 L.
Careful! Do not add 3.4 and 1.25 as if the last digits line up. That would give a wrong answer. The decimal points must line up.
Tip
Same units, then line up. Change to one unit first. Line up the decimal points like the buttons on a shirt. When the mL reach 1 000, trade them for 1 L.
Work each one in your exercise book first. Then tap Show answer to check.
325 L + 480 L
Answer: 805 L. 5 + 0 = 5, 2 + 8 = 10 tens (write 0, carry 1), 3 + 4 + 1 = 8.
3 L 400 mL + 2 L 800 mL
Answer: 6 L 200 mL. 400 + 800 = 1 200 mL = 1 L 200 mL. Then 3 + 2 + 1 = 6 L.
6 L 100 mL − 2 L 700 mL
Answer: 3 L 400 mL. Borrow 1 L: 1 100 − 700 = 400 mL. Then 5 − 2 = 3 L.
4.5 L + 2.35 L
Answer: 6.85 L. Write 4.5 as 4.50, then 4.50 + 2.35 = 6.85.
A full 20 L jerrycan is used for cooking. Keza takes out 8.75 L. How much is left?
Answer: 11.25 L. 20.00 − 8.75 = 11.25.
What you learned today
Sources and credits
Written by Ganzaa. The stories, drawings and practice questions are original.
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