Build a Digital Treasure Shop

Build a digital treasure shop to practise two-digit addition and subtraction.

Introduction

30 Second Summary

A treasure purse can look full until the shop asks for coins you do not have in the right sizes. Solving that puzzle makes every coin matter.

In this project, you will build a colourful treasure shop in Polypad by Amplify. Digital tiles make each purchase visible from a starting purse of 50 coins to a checked total of 39.

What You'll Build

You'll show someone a finished treasure-shop picture that traces every coin from the starting purse to the checked total of 39.

By the end of this project, you'll have:

A 50-coin purse that makes place value visible through five tens.
A worked shopping trail that uses subtraction to buy the map. It then trades one ten for ten ones to buy the key.
A finished treasure-shop screenshot that shows 39 coins. The picture includes an addition sentence. It uses subtraction as the inverse operation.
Secret Mission: Design a new purchase from 25 coins. Choose a price that forces another ten trade.

Are there any prerequisites?

You'll need an adult helper plus an internet-connected Mac running macOS 13 Ventura or later. The guide covers Google Chrome setup without requiring a Polypad account.

Before We Start

Before the hands-on work begins, this is your moment to choose the treasure-shop story and tell your adult why you are building it. Your shop gives every number a job while you practise adding and taking away with tens and ones.

Set Up the Treasure Shop

A treasure shop needs a safe canvas where every coin can be moved. This step checks that your Mac can open that canvas before the maths begins.

An adult first confirms that your Mac runs macOS 13 Ventura or later. Then you use Google Chrome to open Polypad by Amplify without an account.

In this step, get ready to:

Prepare Google Chrome on a Mac running macOS 13 Ventura or later.
Open an empty Polypad canvas without creating an account.
Confirm that a number tile can move across the canvas.

Check the Mac and prepare Google Chrome

Google Chrome requires macOS 13 Ventura or later. Your adult can confirm the Mac version before you check whether Chrome is ready.

Ask your adult to confirm that the Mac runs macOS 13 Ventura or later.
Press Command-Space bar to open Mac search.
Enter Google Chrome in the search field.
Press Return to try opening Chrome.

✔️ Chrome opens on a supported Mac

Good, Chrome is ready for your maths canvas.

Keep the Chrome window open for the next substep.

ⓧ Chrome is missing on a supported Mac

Installing a browser changes the Mac's Applications folder. Your adult handles this part with you.

Ask your adult to visit the official Google Chrome download page.
Ask your adult to download Google Chrome.
Ask your adult to open googlechrome.dmg.
Ask your adult to drag Chrome to the Applications folder.
Press Command-Space bar to open Mac search.
Enter Google Chrome in the search field.
Press Return to open Chrome.

Chrome opens in its own window. That gives you the browser needed for Polypad.

ⓧ The Mac needs an update

A macOS update changes the whole computer. Your adult takes care of this system task before the project continues.

Ask your adult to update the Mac to macOS 13 Ventura or later.
Ask your adult to confirm the updated macOS version.
Press Command-Space bar to open Mac search.
Enter Google Chrome in the search field.
Press Return to open Chrome.

Chrome still not opening?

Ask your adult to reopen googlechrome.dmg if the installation did not finish.
Ask your adult to check the Applications folder for Chrome before downloading it again.

Get help with the installation by asking: Why will Google Chrome not open after installation on my Mac?

Open an empty Polypad canvas

Polypad is a digital maths canvas for moving tiles. Most of its content works without an account.

Return to the Google Chrome window from the previous substep.
Click the address bar at the top of Chrome.
Enter https://polypad.amplify.com/ in the address bar.
Press Return to load Polypad.
Choose the option that opens an empty Polypad canvas.
Continue without a Polypad account if a sign-in choice appears.

You'll see an empty canvas with a sidebar for choosing tiles. This is the space where your treasure shop takes shape.

Why use Polypad without an account?

Most Polypad content and features work without an account. The signed-out canvas keeps this project focused on moving coins without sharing personal details.

Test a number tile

A number tile holds a value that you can move around the canvas. Testing one tile proves that Polypad responds to your pointer.

Find the number tiles in the Polypad sidebar.
Drag one number tile onto the middle of the empty canvas.

Before you move the tile, where do you expect it to go when your pointer crosses the canvas?

Drag the test tile to a different part of the canvas.

You'll see the tile follow your pointer to its new position. That movement confirms the canvas is working.

Tile not moving?

Drag the tile itself instead of the empty canvas behind it.
Hold the pointer down while moving the tile.
Reload Polypad if the canvas stops responding.

Get help with the tile by asking: Why is my Polypad number tile not moving?

Select the test number tile.
Choose the delete action from the tile's action bar.

You'll see an empty Polypad canvas again. This is the clean starting point for your treasure shop.

You have the setup sorted: your empty Polypad canvas is ready for its first treasure coins. Next up, you'll build a purse that shows 50 as five tens.

Build a 50-Coin Purse

Your tile test in Google Chrome proved that the Polypad canvas responds to your pointer. You can now turn that empty canvas into the start of your treasure shop.

The shopping story needs a purse with a clear starting value. Showing 50 as five tens makes place value visible before the shopping begins.

In this step, get ready to:

Name the treasure shop on the canvas.
Build a purse containing five tens.
Count the five tens to confirm they represent 50 coins.

Label the treasure shop

Labels give each part of the canvas a job. The purse holds available coins while the bought area records future purchases.

Switch back to the unsigned-in Polypad canvas from earlier in Google Chrome.
Select the Text tool from the toolbar.
Click near the top of the empty canvas.
Type My Treasure Shop.
Click below the title on the left side of the canvas.
Type Purse.
Click below the title on the right side of the canvas.
Type Bought.

You should see My Treasure Shop at the top. The Purse label should sit to the left of Bought.

Build five tens

A tile worth 10 represents one group of ten coins. Five of these tiles show 50 without any loose ones.

Find the number tiles in the sidebar.
Drag one number tile worth 10 below the Purse label.
Repeat the same drag until the purse contains exactly five tiles worth 10.
Arrange the five tiles in a neat row.

That first model is in place. Your purse now shows five separate tens that you can count and move.

Can't See Five Tens?

Check that every tile in the purse shows 10.
Select any extra tile.
Choose the delete action from the action bar.

Help me fix the number tiles in my Polypad purse.

Label and count the purse

The final label connects the picture to its total. Counting by tens checks that the model matches the number 50.

Select the Text tool from the toolbar.
Click beneath the five tiles in the Purse area.
Type 50 coins.

Before the final check, what total do you expect to reach when you count the five tiles by tens?

Point to each tile from left to right.
Count 10, 20, 30, 40, 50 aloud.
Explain to your adult that five tens equal 50.
Check that the Bought area contains no tiles.

You should see My Treasure Shop, Purse, Bought, and 50 coins on the canvas.

The purse should hold exactly five 10 tiles in a neat row. The bought area should still be empty.

Your purse now makes 50 visible as five tens. Next up, you will spend some of those coins on the treasure shop's first purchase.

Buy the Map and Meet a Tricky Payment

Your Polypad purse already shows 50 coins as five tens. Now the treasure shop needs its first two purchases.

The 20-coin map creates a straightforward first sale. The 18-coin key then tests whether your current tiles can show its exact price.

In this step, get ready to:

Pay 20 coins for the treasure map using two tens.
Record the map purchase as 50 - 20 = 30.
Test whether the three remaining tens can pay exactly 18 coins.

Pay 20 coins for the map

The map costs 20 coins. Two complete tens make that amount exactly.

Return to the Polypad canvas from the previous step.
Select the Text tool in the toolbar.
Click an empty spot near the Bought area.
Type Treasure Map: 20 coins.
Click an empty part of the canvas to finish the label.
Drag one 10 tile from Purse to Bought.
Drag a second 10 tile from Purse to Bought.

You should see two 10 tiles in Bought. That first sale works cleanly because 20 is two complete tens.

Record what remains

A subtraction number sentence records the starting amount. It also shows the amount spent plus the amount left.

Select the Text tool in the toolbar.
Click an empty spot below the map label.
Type 50 - 20 = 30.
Click an empty part of the canvas to finish the number sentence.
Count the three remaining tens aloud as 10, 20, 30.

You should see three 10 tiles left in Purse. Together they represent the 30 coins that remain.

Try the 18-coin key payment

The key costs 18 coins. An exact payment uses one ten plus eight individual ones.

Select the Text tool in the toolbar.
Click an empty spot near the map label.
Type Magic Key: 18 coins.
Click an empty part of the canvas to finish the label.
Point to each remaining 10 tile in Purse.
Count the purse aloud as 10, 20, 30.

Before you test the key payment, picture whether the tiles in Purse can supply eight ones.

Point to one 10 tile as the tens part of the planned payment.
Look in the Purse area for eight 1 tiles.

You will find zero 1 tiles in Purse. The planned 18-coin payment stops here.

This shortfall is intentional. Your canvas now shows why three tens cannot make an exact payment of 18 without ones.

Your canvas should show Treasure Map: 20 coins, 50 - 20 = 30, and Magic Key: 18 coins.

Bought should contain exactly two 10 tiles. Purse should contain exactly three 10 tiles plus zero 1 tiles.

Does Your Canvas Look Different?

Move any third 10 tile from Bought back to Purse.
Select any extra 1 tile that was added during this step.
Choose Delete in the action bar.

Help me restore the correct treasure-shop canvas.

Your shop now shows exactly why the 18-coin key is tricky. Next up, you will find a way to make the missing ones without changing the value of the 30 coins.

Trade a Ten to Buy the Key

Your map purchase left 30 coins in the Purse. The key costs 18 coins, but the three remaining tens cannot make the eight ones you need.

Trading fixes this problem by changing one ten into ten ones. The value inside the Purse stays at 30 coins during the trade.

In this step, get ready to:

Trade one ten for ten ones without changing the value of the Purse.
Pay exactly 18 coins for the magic key.
Show the 12-coin remainder with its subtraction sentence.

Trade one ten for ten ones

One 10-value tile carries the same amount as ten 1-value tiles. This use of place value changes the tile shapes while keeping the Purse total at 30.

This trade takes careful tile selection, so move slowly through the controls.

Select one of the three 10-value tiles in the Purse area.
Choose the split action from the controls beside the selected tile.
Point to each new 1-value tile as you count from 1 to 10.

You have cleared the tricky part. The Purse now shows two 10-value tiles plus ten 1-value tiles.

What is regrouping?

This trade is called regrouping. Regrouping changes how an amount is organised so you can subtract using smaller place-value units.

The tiles look different after the trade. Their total value remains 30.

Pay 18 coins for the key

The number 18 contains one ten plus eight ones. Your traded tiles now give you both place-value parts of that payment.

Drag one of the two remaining 10-value tiles from Purse to Bought beside Magic Key: 18 coins.
Drag eight 1-value tiles from Purse to the key payment in Bought.
Count the key payment as one ten plus eight ones.

The key is now paid for with exactly 18 coins. The Purse holds one ten plus two ones.

Key Payment Not Showing 18?

The key payment needs one 10-value tile plus eight 1-value tiles.

Count the 1-value tiles beside the key label.
Move any extra 1-value tiles back to Purse.
Move any missing 1-value tiles from Purse to Bought.

Help me check my key payment.

Show the 12 coins left

The remaining tiles show 12 as one ten plus two ones. A number sentence connects that tile model to the subtraction you completed.

Drag the two remaining 1-value tiles next to the remaining 10-value tile in Purse.

You should now see one ten plus two ones grouped together in the Purse.

Use the Text tool in Polypad to add 30 - 18 = 12 beside the key purchase.

Before you count, predict whether the key payment plus the remainder will match the new subtraction sentence.

Count the key payment as one ten plus eight ones.
Count the remaining coins as one ten plus two ones.
Say 30 - 18 = 12 to your adult.

Your payment count lands on 18. Your remainder count lands on 12.

That trade has solved the payment problem. The tile model now matches 30 - 18 = 12.

Your magic key is paid for with a complete regrouping model. Next, you will open the treasure chest and add its bonus coins to the 12 coins left in your Purse.

Open the Treasure Chest

Your key purchase left 12 coins in the Polypad purse. The treasure chest now adds a reward to the same model.

Adding 27 shows how tens and ones combine to make 39. An inverse operation then checks the total by taking the bonus away.

In this step, get ready to:

Add a 27-coin treasure chest bonus to the 12 coins in the purse.
Prove the final total with an addition sentence plus its subtraction check.
Capture the finished treasure shop as a Mac screenshot.

Add the chest bonus

The bonus begins as two tens plus seven ones. Keeping those tiles beside the existing 12 makes each part of the addition visible.

Use the Text tool in the toolbar to add Treasure Chest Bonus: 27 coins beside the Purse area.

You should see the new chest-bonus label beside the coins left after buying the key.

Drag two new 10-value number tiles from the sidebar beside the 12 coins in Purse.
Drag seven new 1-value number tiles from the sidebar beside the two new tens.
Count the bonus tiles as two tens plus seven ones.

You should count 20 from the two tens. The seven ones bring the chest bonus to 27.

Combine and check the total

The existing 12 joins the 27-coin bonus in one place-value model. Subtraction can then check the addition by removing the amount that was added.

Arrange every tile in Purse as three 10-value tiles above nine 1-value tiles.
Count the three tens as 10, 20, 30.
Count the nine ones from 31 to 39.

You should finish at 39. The purse now shows the final treasure total as three tens and nine ones.

Use the Text tool to add 12 + 27 = 39 beside the completed purse.

Before you check the addition, what amount do you think will remain when the 27 bonus coins are moved aside?

Temporarily move the two bonus tens plus the seven bonus ones away from the purse group.
Count the tiles that remain in the purse.

You should see one ten plus two ones. That gives you 12 again, so the addition passes its subtraction check.

Return the 27 bonus coins to their places in the purse.
Use the Text tool to add 39 - 27 = 12 below the addition sentence.

The Purse should again show exactly three tens and nine ones. The canvas should show both new number sentences beside the unchanged map and key payments in Bought.

Capture the finished shop

An unsigned-in Polypad canvas is not saved to an account. A Mac screenshot gives you a copy of the finished treasure story.

Framing the whole canvas can feel fiddly, so your adult can help you place the crosshair.

Check with your adult that the title, purse, bought area, final 39-coin model, and number sentences all fit on the screen.
Press and release Shift-Command-4.
Drag the crosshair from one corner of the finished canvas to the opposite corner.
Release the pointer to capture the selected area.
Move the Google Chrome window aside to view the Mac desktop.

You should see a timestamped PNG screenshot on the desktop. Open it to confirm that the finished 39-coin model plus both number sentences are visible.

Can't find the screenshot?

Press Shift-Command-4 again to restart the capture.
Drag around the full canvas before releasing the pointer.

Ask for help with the capture if the new file still does not appear. Help me find the screenshot I captured on my Mac.

You did it. Your screenshot now preserves the complete treasure story from 50 coins to the checked total of 39.

Secret mission

Design Your Own Tricky Deal

Your original treasure shop proves one trade. Now you will invent a new 25-coin purchase that needs another trade. You will prove the change with tiles, a subtraction sentence, and a second screenshot.

Clean Up Your Resources

Your unsigned-in Polypad session has no ongoing costs. Decide whether to keep the canvas open, close it while preserving your screenshots, or delete every project copy.

Resources you used:

The live unsigned-in Polypad canvas containing the original 39-coin shop plus the new 25-coin deal.
The first timestamped PNG screenshot showing the original treasure shop.
The second timestamped PNG screenshot showing the new tricky deal.

Keep everything running

No action needed. This option keeps the live canvas editable plus both screenshots ready to share.

Leave the current Polypad tab open so the unsigned-in canvas stays editable.
Keep the first timestamped PNG screenshot on the Mac desktop as your record of the 39-coin shop.
Keep the second timestamped PNG screenshot on the Mac desktop as your record of the new tricky deal.

Pause - I'll come back to this later

Choose this when editing is complete. Both screenshots stay on the Mac desktop.

Closing the tab ends the editable session. Your screenshots preserve a picture of everything you built.

Confirm that the first timestamped PNG screenshot shows the original 39-coin treasure shop.
Confirm that the second timestamped PNG screenshot shows the new 25-coin tricky deal.
Close the Polypad tab after both checks.

Delete - I don't want to use this again

This option removes every project copy. Your Mac keeps everything else unchanged.

Close the current Polypad tab to discard the unsigned-in canvas.
On the Mac desktop, select the two timestamped PNG screenshots from this project.
Drag the selected screenshots into the Trash.
Empty the Trash to remove the screenshots permanently.
Check the Mac desktop to confirm that neither timestamped project screenshot remains.

Nice Work!

Fantastic work on completing your digital treasure shop in Polypad. Your two Mac screenshots preserve the checked 39-coin total plus your own tricky deal.

Here's what you learned:

Represented place value by building 50 from five ten-value tiles.
Used regrouping to trade one ten for ten ones. That trade made the magic key payment in 30 - 18 = 12 possible.
Added the 27-coin bonus to reach 39 coins. Used the inverse operation 39 - 27 = 12 to check the total.
Completed the Secret Mission by designing a new 25-coin deal with a price from 16 to 19 coins. Proved the leftover amount with another trade.

Ready to quiz yourself?