## Make a coin sorter

Hold one end of the cardboard up and roll a coin down the groove. Which hole does it fall through?

Safety: This activity uses a sharp scalpel. Younger mathematicians should ask an adult to help.

You will need

• Corrugated cardboard
• Scalpel
• Cutting mat
• Sharp pencil or pen
• Rubber bands
• \$2, \$1 and 20c coins

What to do

1. Cut a piece of corrugated cardboard about 25 cm long and 10 cm wide. Make sure the corrugations are running along the length of your rectangle.
2. Fold the long side of the cardboard, about 2 cm from edge. Then make another fold about half a centimetre further in from that fold.
3. Put rubber bands around the cardboard to hold the folds. If you look at the cardboard from the side, it will be in a j shape that creates a groove for the coins to sit in. Put some coins in the folded cardboard and tilt it. The coins should roll freely along the groove.
4. Make 3 marks along the groove, each 5 cm part.
5. Put a \$2 coin in the groove near the first mark. Draw a line about 1 cm above the top of the coin, and 2 lines each 5 mm from each side of the coin. Label this hole, ‘\$2’.
6. Put a \$1 coin in the groove near the second mark. Again, draw a line about 1 cm above the top of the coin, and 2 lines each 5 mm from each side of the coin. Label this hole, ‘\$1’.
7. Then put the 20c coin in the groove near the final mark, and draw lines around it as well. As per previous steps, draw a line about 1 cm above the top of the coin, and 2 lines each 5 mm from each side of the coin. Label this hole, ‘20c’.
8. Remove the coins and rubber bands, and then unfold the cardboard.
9. Look at the lines you drew around the \$2 coin. Draw a line about 5 mm from the creases in the cardboard, and then join up the 4 lines to make a rectangle. Do this for the lines for the \$1 and 20c coins also.
10. Use your scalpel to cut out the 3 rectangles.
11. Put the rubber bands back on to hold the cardboard in place.
12. Hold the cardboard with the folds towards the ground, and the end with the smallest hole slightly elevated. Put a coin in the groove on the elevated side and watch it roll down. Which hole does it fall through?

What’s happening?

In this activity you’ve sorted coins of different values based on their size. Money around the world comes in lots of different shapes and sizes. But whether you’re looking at Euros, Pounds or Yen, there are some striking similarities. Notes are almost always more valuable than coins. And within a currency, different valued coins will be different shapes or sizes.

Different valued coins have to be recognisable – otherwise you have no way of knowing what they’re worth. So coins have different colours and patterns on them to make them easy to recognise. However different sized coins don’t just look different – they also feel different.

As coins are different sizes, you can identify them by touch alone. This helps if you want to get change out of your pocket, but it’s also important for people who have difficulty seeing. Different sized coins mean you don’t have to see in order to use money.

Counting coins isn’t the only time people use their sense of touch to do maths. In 1952, Abraham Nemeth created a version of Braille for mathematicians. It can be very hard to read equations aloud, so mathematical Braille makes learning and doing maths a lot easier for blind mathematicians.

 You will need a 25 cm x 10 cm piece of corrugated cardboard.
 Fold up one edge and hold it in place with rubber bands. Make 3 marks about 5 cm apart.
 Place a \$2 coin in the groove near the first mark. Draw lines 1 cm above and 5 mm beside it. Repeat for the other coins on other marks
 Cut 3 rectangles out of the cardboard, and fold it up again.
 Hold one end of the cardboard up and roll a coin down the groove. Which hole does it fall through?

Article source: http://www.csiro.au/

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