Mini Minds Hub · Free printable
Best Buy Detective: Free Printable Worksheet for Year 7
- ForYear 7
- StageKey Stage 3
- CostFree
- FormatPrintable PDF
Best Buy Detective is a free printable maths worksheet for Year 7 (ages 11 to 12), in Key Stage 3. Children work out the unit price on each receipt, then use their results to catch the one shop that is overcharging. It needs only a pencil, and page 2 gives the grown-up notes, help ideas, a stretch task and the answers.
It comes from the Mini Minds Hub, the free library of printables from Jaques of London, the British games and toy company that has been making games for families since 1795. Print both pages, give page 1 to your child and keep page 2 for yourself. Black and white printing works well.
What is on the sheet
Children fill in a table with the columns Shop, Item, Weight, Paid and Price per kg. They work out the price per kg for each receipt, then use the table to name the shop that is overcharging and the item. Numbered questions follow, with space to answer. Children find what a weight should cost at the shelf price, work out the overcharge, and write it as a percentage of the correct price.
- Shop
- Item
- Weight
- Paid
- Price per kg
- Which shop is the culprit? Name the item too.
- What should 0.75 kg of cheese cost at the shelf price?
- How much was the customer overcharged?
- Write the overcharge as a percentage of the correct price.
Worked example: finding a price per kg
A shopper pays £2.10 for 1.5 kg of potatoes. What is the price per kg?
This is a different question from the sheet. Use it to show the method, then let your child try the receipts alone.
Method 1: divide the price by the weight- Price per kg means the cost of 1 kg, so divide the amount paid by the number of kilograms.
- Work out £2.10 ÷ 1.5.
- Multiply both numbers by 10 to make it easier: 21 ÷ 15 = 1.4.
- So the price is £1.40 per kg.
- 1.5 kg is three lots of 0.5 kg.
- Divide the price by 3: £2.10 ÷ 3 = £0.70 for 0.5 kg.
- 1 kg is two lots of 0.5 kg, so double it: £0.70 × 2 = £1.40.
How the detective work goes
Step 1: fill the table
Complete the Price per kg column for every receipt. Show the division each time, so the working can be checked.
Step 2: compare
Once every price per kg is in the table, look for the one that does not fit the pattern of the shelf price.
Step 3: scale a quantity
Use the shelf price per kg to find what a different weight should cost. Multiplying a price per kg by a weight gives the cost.
Step 4: measure the gap
Subtract the correct cost from the amount paid. Then compare that gap with the correct price to get a percentage.
Why unit prices matter
Shops sell the same kind of item in many pack sizes and weights. A bigger pack has a bigger price, but that does not tell you which one is better value. A unit price puts everything on the same scale, such as the cost of 1 kg. Then two items can be compared fairly, even when their weights are very different.
Unit pricing is proportional reasoning in daily life. If the weight doubles, the fair price doubles too. Spotting when a price does not follow that rule is a useful skill for any shopper. It also prepares Year 7 children for ratio, rates and percentages, where they compare quantities and explain which is larger and by how much.
Shopping facts
- Many UK shops show a unit price on the shelf label, such as the price per kg or per 100 g.
- There are 1000 grams in 1 kilogram.
- The word percent means per hundred.
- A bigger pack is not always the cheapest per kg, so it is worth checking the unit price.
- Multiplying a price per kg by a weight in kg gives the cost of that weight.
Skills and curriculum link
- Unit pricing
- Proportional reasoning
- Comparing best buys
- Dividing with decimals
- Percentages of an amount
- Showing working
Ideas that help
- Price per kgThis is the cost of one kilogram. To find it, divide the amount paid by the weight in kilograms.
- ScalingIf you know the cost of one amount, you can find the cost of another by multiplying or dividing in the same way on both sides.
- OverchargeThis is the difference between what was paid and what should have been paid.
- Percentage of the correct priceTo compare a difference with a starting amount, divide the difference by that starting amount, then multiply by 100.
Key words
- Unit priceThe price for one unit, such as 1 kg.
- ProportionalChanging together at the same rate. If the weight doubles, the price doubles.
- OverchargeTo ask for more money than the correct price.
- PercentageAn amount shown as parts out of 100.
- ReceiptA printed record of what was bought and how much was paid.
- Best buyThe choice that gives the lowest cost for each unit.
How to use it
- Print both pages. Page 1 is for your child. Keep page 2, which has the notes and answers.
- Ask your child to complete the table first. Each price per kg needs a division, and they should show it.
- Use the finished table to name the culprit. Ask them to explain how they know, using the numbers.
- Work through the numbered questions together the first time. Talk about each choice of method.
- Check against page 2. Come back another day to repeat the tricky parts, because a familiar task builds confidence.
Help, stretch and game ideas
If it feels too hard
Change 0.25 kg and 0.75 kg into grams first, which can make the numbers easier to picture. Or find the price per kg by doubling or scaling up from the weight shown. Do one receipt together, then let them try the next alone.
To stretch confident children
Invent a fourth receipt where a shop overcharges on a different item. Choose the shelf price first, then change the amount paid so it is too high. Swap it with a partner and ask them to catch the culprit and work out the percentage overcharge.
Make it a game
Play shop inspectors. One pupil reads a receipt aloud, giving the item, weight and amount paid. The other checks it against the shelf price per kg and announces a verdict: fair price or overcharged. Swap roles and keep a score of correct verdicts.
Mistakes to watch for
Watch forA child divides the weight by the price instead of the price by the weight, so the answer looks far too small.
Try thisAsk what the answer should mean: pounds for each kilogram. Then check that dividing the pounds by the kilograms gives that.
Watch forA child reads 0.25 kg as 25 g or 0.75 kg as 75 g.
Try thisRemind them that 1 kg is 1000 g. Write 0.25 kg as a fraction of a kilogram, or convert it to grams before dividing.
Watch forA child writes the overcharge as a percentage of the amount paid, not of the correct price.
Try thisReread the question together. Underline the words correct price and use that amount as the starting point for the percentage.
Talk about it
- How did you decide which receipt to work out first?
- What does price per kg tell you that the amount paid does not?
- Is there a way to check your division using multiplication?
- Why might a shop show the unit price on its shelf labels?
- If a weight doubles, what should happen to the price?
- When have you seen a deal that looked cheap but might not be?
Take it off the page
Shelf label hunt
On a shopping trip, look at the unit price on shelf labels. Pick two similar items and ask which one costs less per kg or per 100 g.
Price list
Make a pretend shop price list with a price per kg for five items. Ask someone to choose weights and work out the cost of each.
Pack size check
Choose two pack sizes of the same product from the cupboard. Use the weight and price on the labels to work out which is better value.
Who it is for
Parents
Sit with your child for the first receipt, then let them lead. Ask them to explain each division out loud. If they get stuck, try the grams idea on page 2. Praise careful working as well as right answers.
Teachers
Use it as a starter, a plenary, an early finisher task, homework or a table activity. It needs no preparation beyond printing. Page 2 gives support and stretch for mixed ability groups, and the table makes reasoning easy to see in books.
Home educators
Print it as part of a wider maths plan and pair it with real shopping. Children can check unit prices on real shelf labels. The sheet is free to print again for brothers and sisters, or for revision a few weeks later.
Where this fits
Before this, children build on Key Stage 2 work with division, decimals, fractions and simple percentages. They also need to know the metric units for mass, such as grams and kilograms. Confident times tables help when scaling a price up or down.
After this, the same thinking grows into ratio, proportion and rates of change. Children compare quantities in more formal ways, use percentages in a wider range of problems and explain their reasoning. Unit prices are an early, practical example of a rate.
Questions parents and teachers ask
- What age is Best Buy Detective for?
It is written for Year 7 (ages 11 to 12), in Key Stage 3. It can also work as revision for confident Year 6 pupils, or as support for older children who need more practice with unit prices.
- What will children practise?
Children practise finding unit prices, scaling quantities in proportion and comparing best buys. They also use percentages to describe an overcharge. All of it uses money problems that link to real shopping.
- Can children use a calculator?
Yes, calculators are optional. Whether to use one is up to you. Either way, ask children to show the division for each price per kg, so you can see their method as well as the answer.
- What if the sheet feels too hard?
Start by changing the weights into grams, or find the price per kg by doubling or scaling up from the weight shown. Work through the first receipt together, then let your child try the next one alone.
- Is it free?
Yes. It is free to print for home and classroom use. You can print it again for brothers and sisters, or for revision later on.
- Can teachers use it in class?
Yes. Teachers can use it as a starter, plenary, early finisher task, homework or table activity. It needs no preparation beyond printing, and page 2 has support and stretch ideas for mixed ability groups.
- Is it screen free, and do I need colour?
Yes, it is screen free and needs only paper and a pencil. You do not need colour either. It prints well in black and white on plain A4 paper, so it is cheap to use at home or in school.
Preview the full PDF
Made by Jaques of London, making games for families since 1795. A printable supports classroom learning and does not replace a teacher.