Addition and Subtraction to 1000
Primary 3 · Mathematics
Addition and Subtraction to 1000
Lesson 3 of 3
14 min
Umutoni's mother sells avocados at the market in Kigali. On Saturday she sold 185. On Sunday she sold 236.
Umutoni knows how to add. She knows how to subtract. But which one does this story need?
That is the real skill: reading a story and choosing the right operation. Let's practise it together.
Every time, ask yourself:
Only then do you decide: is something being joined together, or is something being taken away or compared?
A school collected 246 plastic bottles on Monday and 178 bottles on Tuesday. How many bottles altogether?
The two piles are being pushed into one big pile. Joining means add.
246 + 178: ones 6 + 8 = 14, write 4 carry 1. Tens 4 + 7 + 1 = 12, write 2 carry 1. Hundreds 2 + 1 + 1 = 4.
Answer: 424 bottles.
A shop had 500 exercise books. It sold 274 of them. How many are still on the shelf?
Books are leaving the shop. Taking away means subtract.
500 − 274: borrow across the zeros, so the ones become 10, the tens become 9 and the hundreds become 4. Ones 10 − 4 = 6. Tens 9 − 7 = 2. Hundreds 4 − 2 = 2.
Answer: 226 exercise books. Check: 226 + 274 = 500. Correct!
Keza has saved 348 Frw. A story book costs 500 Frw. How much MORE money does she need?
Nothing is being taken away here — we are comparing two amounts and looking for the gap between them. The gap is always found by subtracting the smaller from the bigger.
500 − 348 = 152 Frw. Keza needs 152 Frw more.
Now back to the market. Umutoni's mother started the weekend with 600 avocados. She sold 185 on Saturday and 236 on Sunday. How many are left?
You cannot answer this in one sum. It needs two steps, and the order matters.
Step 1 — how many did she sell in total? The two days join together, so add.
185 + 236: ones 5 + 6 = 11, write 1 carry 1. Tens 8 + 3 + 1 = 12, write 2 carry 1. Hundreds 1 + 2 + 1 = 4.
She sold 421 avocados.
Step 2 — how many are left? The sold ones have gone away, so subtract them from what she started with.
600 − 421: borrow across, ones become 10 and tens become 9, hundreds become 5. Ones 10 − 1 = 9. Tens 9 − 2 = 7. Hundreds 5 − 4 = 1.
Answer: 179 avocados are left.
Notice the danger: if you stopped after Step 1 you would answer 421, which is how many she sold, not how many are left. Always read the question again at the end and check you answered what was actually asked.
Tip
Tell the story back, then choose. Say it in your own words: "She had some, some went away…" → subtract. "She had some, more came…" → add. "Who has more, and by how much?" → subtract.
And ask: should my answer be bigger or smaller than the number I started with? If the avocados are being sold, the answer must be smaller than 600. If your answer came out bigger, you added when you should have subtracted.
For each story, first say whether you will add or subtract. Then work it out in columns.
What you learned today
Quick check
Gatete has 300 Frw. A ball costs 450 Frw. How much more money does he need?
