Measuring Length up to 10 m
Primary 1 · Mathematics
Measuring Length up to 10 m
Lesson 5 of 5
13 min
Let's begin
On umuganda day the neighbours clear the path to the water tap.
Habimana has a rope 6 m long and a short rope 3 m long.
He ties them together to mark the whole path.
Today you will add and take away metres.
Worked example
6 m and 3 m tied together.
Step 1 Look at the numbers only: 6 and 3.
Step 2 Add them: 6 + 3 = 9.
Step 3 Put the m back: 9 m.
6 m + 3 m = 9 m
Say it in words: 6 m and 3 m make 9 m.
Habimana's new rope reaches 9 m along the path.
Careful! Never leave the m out. 9 on its own does not say how long.
Worked example
a rope 7 m long. Keza cuts off 4 m.
Step 1 Look at the numbers: 7 and 4.
Step 2 Take away: 7 − 4 = 3.
Step 3 Put the m back: 3 m.
7 m - 4 m = 3 m
Careful! Some children answer 11 m. They added by mistake.
The rope got shorter. So the answer must be smaller than 7 m.
Check by adding back: 3 m + 4 m = 7 m. It works!
Mugisha needs a path 10 m long. He has cleared 4 m already.
4 m + ___ = 10 m
Start on 4. Count on to 10: 5, 6, 7, 8, 9, 10.
That is 6 jumps. The missing length is 6 m.
Check it: 4 m + 6 m = 10 m.
This year all your lengths stop at 10 m.
Tip
Add the numbers. Keep the m
The m never joins the sum. It waits, then comes back at the end.
Tying ropes means add. Cutting a rope means take away.
Watch the first minute only: 20 m + 35 m = 55 m. Stop when the big numbers start.
Do each one, then tap Show answer to check.
5 m + 4 m
Answer: 9 m. 5 + 4 = 9, then put the m back.
10 m - 2 m
Answer: 8 m. 10 − 2 = 8. The length got shorter.
2 m + 3 m + 1 m
Answer: 6 m. 2 + 3 = 5, and 5 + 1 = 6.
Mutesi has a rope 9 m long. She cuts off 5 m. How much rope is left?
Answer: 4 m. 9 − 5 = 4. Check it: 4 m + 5 m = 9 m.
Uwase's fence needs 10 m of wire. She has 7 m. How much more does she need?
Answer: 3 m. Start on 7 and count on: 8, 9, 10. That is 3 jumps.
What you learned today
Two free story books say long and short in Kinyarwanda, the language you speak at home.
Umugabo muremure cyane is about a very tall man whose hoe, door and bed are all ngufi cyane - far too short for him - until he makes each one muremure. It is from African Storybook, free to read.
Gakuru na Gatoya asks who in your family is tall and who is short. It is from the Global Digital Library, also free. After you read it, stand back to back with someone at home and check.
Quick check
