Word problems on subtracting · Martinとコード

Stories where something is taken away or compared. You will spot minus and solve it.

When the story takes away

“Mum baked 24 cakes. The family ate 9 of them. How many cakes are left?”

Something was taken away. The story smells of minus.

Subtracting hides in problems behind words: ate, lost, drove away, broke, spent, flew away, left. And also behind comparing questions: how many more, how many less, how much dearer.

You know the method from the last lesson and it is the same: read twice, write the question, answer in a sentence. Only the sign changes.

Minus stories are everywhere in life. You spent part of your pocket money — how much is left? You read half a book — how many pages are left? Your brother is ten and you are seven — how many years older is he? All subtracting. Today you will learn to find it safely in a story and write it correctly.

Watch one thing: with minus the order matters. You always start with what there was at the start, and take away. 24 − 9, never 9 − 24.

Sofie solves a problem: “There were 15 flowers in a vase, 6 wilted. How many are left?” She writes 15 − 6 = 9 and answers in a sentence. Adam has a trickier one: “Jonáš has 30 Kč, a toy car costs 45 Kč. How much is he missing?” Adam hesitates: “Nothing was taken away here…” Sofie advises: “They are asking for the difference. How many steps are left from thirty to forty-five?” Adam fills up: 30 and 15 is 45. “He is missing 15 Kč!” Missing is subtracting too — just in disguise. He draws stairs from thirty up to forty-five. Fifteen stairs. “Now I see it,” he says. The picture lit up the problem.

💡

You spot minus twice: when something is taken away (ate, lost, left) and when they ask for a difference (how many more, how much is missing).

Two kinds of minus stories

Kind one: taking away. There was — some went — some are left. “There were 24 cakes, 9 were eaten.” Question: 24 − 9 = 15. 15 cakes are left. You always start with what there was at the start (24), and take away.

Kind two: comparing and missing. Nothing disappears, but they ask for a difference. “Tereza has 12 stickers, Ema 8. How many more does Tereza have?” Question: 12 − 8 = 4. Or: “You have 30 Kč, a toy costs 45 Kč. How much is missing?” Difference: 45 − 30 = 15.

The method is still the same, three steps:

Read twice. What was there? What happened (or what is compared)? What are they asking?
Write the question. Bigger number at the front, what you take away after minus.
Answer in a sentence and check the sense: after taking away there must be less left than there was.

If you do not know what to do, draw: 24 circles, cross out 9, count the ones not crossed. Crossing out is subtracting on paper.

And a last weapon: check by adding. 15 left and 9 eaten? 15 + 9 = 24. Exactly as many as there were. The problem matches.

There were 20 felt-tips in a box. 7 do not write any more. How many felt-tips write?

What there was: 20 felt-tips. What happened: 7 dried — some were taken away. They ask: how many write.

Question: 20 − 7 = 13.

From a full ten… actually two: 20 − 7 = 13.

Answer: 13 felt-tips write.

Check by adding: 13 + 7 = 20. It matches. And sense: 13 < 20, some were taken away. That matches too.

A book has 48 pages. Tereza has read 25. How many pages does she have left?

What there was: 48 pages. What happened: 25 read. They ask: how many are left.

Question: 48 − 25 = ?

In parts: 48 − 20 = 28, then 28 − 5 = 23.

Answer: Tereza has 23 pages left to read.

Check: 23 + 25 = 48? Tens 40, ones 8. Yes, 48. It matches.

Filip has 26 Kč. A ball costs 40 Kč. How many Kč is he missing?

Nothing was taken away — this is a missing problem. I ask: how many steps from 26 to 40?

Question: 40 − 26 = ? Or I fill up: 26 + 4 = 30, 30 + 10 = 40. Together 4 + 10 = 14.

Answer: Filip is missing 14 Kč.

Check: 26 + 14 = 40. Exactly the price of the ball. It matches.

⚠️

With minus never swap the numbers by the order they come in the text! “She ate 9 of 24 cakes” — in the text nine comes first, but the question is 24 − 9. At the front is always what there was in all.

Practice: now you do it 🎲

Now try it for real. You will see all the questions at once, like on paper. スタート with ten. If it goes well, add more.

Practise subtracting to 100 — the base for every minus problem.

Practise the questions

On paper

Paper and a pencil. Three steps for each problem, a check by adding at the end.

Solve: 35 cars stood in the car park. 12 drove away. How many cars stayed?
Solve: Ema is 128 cm tall, Adam 121 cm. How many cm taller is Ema?
Solve: A notebook costs 30 Kč. You have 22 Kč. How much are you missing?
Check each result by adding and write the answer in a full sentence.

Now you 💪

I spot a taking-away problem and a comparing problem.
In the question I write at the front what there was in all.
I check the result by adding.

✅

Done when: You solve all three kinds: how many left, how many more, how much is missing — and the checks match.

What to take from this lesson

Minus in a story: ate, lost, drove away, left.
Difference and missing are minus too: how many more, how much is missing.
At the front is always what there was in all. Do not swap the order.
After taking away there must be less left. Check the sense.
Check by adding: left + taken away = there was.