Fractions and percentages: sharing a birthday cake
Cut a cake into equal pieces, take some, and see the same share as a fraction, a decimal and a percentage.
Core concept
In short: Cut a cake and write the same share as a fraction, a decimal and a percentage.
A fraction, a decimal and a percentage can describe the same share of a whole
Topic: Fractions and percentages
A fraction: A part of a whole, written like ¾: the bottom number says how many equal parts, the top how many you take. All key words tells us how many equal pieces of a whole we have. In 3/4, the bottom number (4) is how many equal pieces the whole is cut into, and the top number (3) is how many pieces we take. The same share can be written in different ways: 2/4 and 1/2 are equivalent fractions, because they cover the same amount of cake. Dividing the top by the bottom gives a decimal: A number with a point, like 2.5, where the digits after the point are tenths, hundredths … All key words (1/2 = 0.5), and a percentage says how many parts out of 100 (0.5 = 50%).
What you will learn
- Write the share of a whole as a fraction.
- Find equivalent fractions and write a fraction in its simplest form.
- Change a fraction into a decimal and a percentage.
Before you start
- Divide a number by a small whole number.
Materials
- A round cake (or a paper circle) and a knife
Equipment
- A 100-square grid
Procedure
- Tap − or + to cut the cake into fewer or more equal pieces.
- Tap a piece to take every piece up to it; tap the last piece taken to put it back.
- Record half the cake when it is cut into 4 or more pieces.
- Record a quarter of the cake, 20% of the cake and three quarters of the cake.
How this simulation is simplified
- All the pieces of the cake are exactly the same size.