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Word problems and multi-step logic
Choosing the operation, bar modelling and working through several steps.
Word problems hide the maths inside a story. The calculations are ones you already know. The skill is working out which calculations to do, and in what order. In this lesson you will learn:
- a simple plan for any word problem
- how to choose the right operation: +, −, × or ÷
- how to draw a bar model to see what is going on
- how to break a problem into steps
- how to work backwards to find a starting number
1. A plan for every word problem
- 1Read it twice. Underline the numbers and the question at the end.
- 2Picture it. Draw a quick bar model or sketch.
- 3Plan it. What do you need to find first? Then what?
- 4Solve it, one step at a time. Write each step down.
- 5Check it. Did you answer the question asked? Is the answer sensible? Units: £, cm, pupils?
2. Choosing the operation
| What is happening? | Operation | Clue words |
|---|---|---|
| Putting together, finding a total | + | altogether, total, sum, more than |
| Taking away, finding a difference | − | left, fewer, difference, how many more |
| Equal groups, repeated adding | × | each, every, times as many, rows of |
| Sharing, or grouping equally | ÷ | share equally, each get, how many groups |
Operation detective: which operation solves the story?
3. Bar models: draw the story
Part and whole
A school has 324 pupils. 158 are girls. How many are boys?
The whole is 324 and one part is 158, so the other part is 324 − 158 = 166 boys.
Comparing
Sam has 46 marbles. Jo has 19 fewer. How many does Jo have?
Jo’s bar is 19 shorter than Sam’s, so Jo has 46 − 19 = 27 marbles.
Equal parts
4 friends share £84 equally. How much does each get?
The bar is split into 4 equal parts, so each part is £84 ÷ 4 = £21.
Times as many
Ella has 3 times as many cards as Finn. Together they have 48. How many does Finn have?
There are 4 equal boxes altogether, worth 48. One box is 48 ÷ 4 = 12, so Finn has 12 (and Ella has 36).
Bar model match: which picture fits the story?
4. Problems with several steps
Example
Tickets cost £7 for adults and £4 for children. 2 adults and 3 children go to the cinema. They pay with a £50 note. How much change do they get?
- First find the adults’ cost.2 × £7 = £14
- Then the children’s cost.3 × £4 = £12
- Add them to find the total.£14 + £12 = £26
- Take the total from £50 to find the change.£50 − £26 = £24
Plan it: tap the steps in the right order
- Tap the step that comes first, then the next. One card at higher levels is a step you do not need.
- Then pick the answer. Two problems with no slips moves you up a level.
5. Working backwards
Example: I think of a number. I multiply it by 3, then subtract 5. The answer is 31. What was my number?
- The last thing done was − 5. Undo it with + 5: 31 + 5 = 36.
- Before that was × 3. Undo it with ÷ 3: 36 ÷ 3 = 12.
Check forwards: 12 × 3 = 36, and 36 − 5 = 31.
Think of a number: run the machine backwards
6. Practice: pick your level
Start with Foundation if you are in Year 4 or just starting. Use rough paper: draw a bar model and write each step. Move up when you are getting most of them right.
The mistakes that cost marks
- Grabbing the numbers and adding them. Every number in the story gets added, whatever is happening. ask what is happening first: putting together, taking away, equal groups or sharing.
- Trusting a clue word without reading the sentence. “7 more than Leo” does not always mean add. read the whole sentence and decide who has more. A bar model makes it clear.
- Stopping one step too early. Finding the total cost (£26) when the question asks for the change. read the question again at the end. Did you answer exactly what it asks?
- Undoing the steps in the wrong order. In “× 3, then − 5”, dividing by 3 first. undo the last step first: + 5, then ÷ 3.
- Mixing up the units. Adding pence to pounds, or giving an answer in the wrong unit. write the unit beside every number in your working.
- Not checking the answer is sensible. 166 boys out of 324 pupils is fine; 482 boys would be impossible. ask: is it bigger or smaller than I expected? Then check with the inverse.
Quick checklist
Tick each one when you can do it without help.
All ticked. Brilliant work! You have finished Lesson 2.5, and Module 2.
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Print these and work through them away from the screen.
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