Here is our class fraction shop. Every price is written a bit differently: some are fractions of a euro, some are decimals, and some are marked with a percent off.

• Book: 1/2 of €10
• Comic: €2.50
• Game: 25% off €8
• Snack: €1.50
• Sticker sheet: 1/5 of €5
• Juice: 50% off €1

Here is today's challenge, and it's a real puzzle: can you spend exactly €10 in this shop, not a cent more or less? Before we work anything out, what would we need to know about each item to be sure we've spent precisely €10?

A €4 item at 50 percent off

Here is our first item. Watch how we read the price tag. The tag says 50% off, and 50% is just another way of writing one half. Half of €4 is €2, so this item really costs €2. We turned the percent into the fraction that was easiest to work with.

A quarter off a €20 voucher

Now the trickier one. This voucher is worth €20 and the tag says a quarter off. A quarter of €20 is €5, so the discount is €5. But careful, that's the amount we take away, not the price we pay. Twenty take away five leaves us paying €15. Predict before I reveal the next one: if the tag had said 0.25 off instead of a quarter off, would anything change?

The same amount, three ways

Here is the key one. A quarter, 0.25 and 25% are the very same amount. That is why the voucher answer is identical whichever form the tag uses. In our shop, the form on the tag is just a disguise. The real price underneath never changes.

Let's build one €8 basket together on the board using items from our shop list. Today we work through these three in order, saying each one's real price aloud before we add it on:

• Book: 1/2 of €10
• Comic: €2.50
• Snack: €1.50

We'll find each real price, keep a running total on the board, and see whether these three land us exactly on €8 — or whether we need to swap one out. If we overshoot, we can swap the snack at €1.50 for the juice at 50% off €1 and see what that does to the total.

Now for the main challenge, working only from our shop list on the board:

• Book: 1/2 of €10
• Comic: €2.50
• Game: 25% off €8
• Snack: €1.50
• Sticker sheet: 1/5 of €5
• Juice: 50% off €1

Turn each disguised price into its real euro amount, then find three different combinations that each total exactly €10. Work them in your copy, keeping a running total as you add each item. The stretch asks whether you could ever buy five of the six items for exactly €10.