Activities/Abacus/Worksheet/Answersheet

Ways to make 1/2
Ways to make 1/2 just using one string



To make 1/2 just using one string, the fraction denominator must be divisible by 2. The string must contain an even number of beads, 2 4 6 8 10 12

Ways to make 1/2 with more than one string

1/3 + 1/6 = (2+1)/6 = 3/6 = 1/2

1/3 + 2/12 = (4+2)/12 = 6/12 = 1/2

1/4 + 1/6 + 1/12 = (3+2+1)/12 = 6/12 = 1/2

1/4 + 2/8 = (2+2)/8 = 4/8 = 1/2

1/4 + 3/12 = (3+3)/12 = 6/12 = 1/2

3/9 + 2/12 = (12+6)/36 = 18/36 = 1/2

2/8 + 3/12 = 1/4 + 1/4 = 1/2

1/6 + 4/12 = (2+4)/12 = 6/12 = 1/2

1/6 + 3/9 = (3+6)/18 = 9/18 = 1/2

1/6 + 2/8 + 1/12 = (4+6+2)/24 = 12/24 = 1/2

2/6 + 2/12 = (2+1)/6 = 3/6 = 1/2

1/5 + 3/10 = (2+3)/10 = 5/10 =1/2

2/5 + 1/10 = (4+1)/10 = 5/10 =1/2

Is this all of the possibilities?

See Diophantine equations, computer programs including ones written in TurtleArt can find all the solutions by trial and error.

You can paste into Turtle Art to calculate all the possibilities

Ways to make 1/3
This program can be modified for 1/3 and 2/3 (and with more work it could be used for the Caacupé abacus). Circled below, the program above has 0.5 replaced with 1/3 to find the ways of making 1/3

4/12

3/9

2/8 + 1/12

1/6 + 2/12

2/6

1/4 + 1/12

1/3

Paint
You need to guess the centre of the circle and angles of the pie slice lines. The full circle or 360 degrees represents '1' so the 1/3 and 1/6 pie slices are 360/3 =120 degrees 360/6 = 60 degrees

You can use either the polar grids of Ruler or TurtleArt  to help visualise the angles

Turtle Art
Copy into TurtleArt to generate the pie for 1/3 + 1/6



It can be modified for other pie slice sizes. The fill command does not work on line arcs, so the pies are not coloured. Here is another solution for coloured pie slices

Socialcalc
Spreadsheets are powerful tools for representing numbers. The Socialcalc Activity (V5) is a little buggy, the menu bars are very cramped. If you have access to Gnumeric in Gnome, it is recommended

Enter the data 1/3, 1/6 and 1/2 into 3 cells, select (grey highlight) the 3 cells



Click the graph tab, select 'Pie Chart'



The Caacupé abacus
We have not given answers here for the Caacupé abacus. There are a lot more solutions. Trial and error could take a long time. The TurtleArt program above could be modified to generate solutions.