Spinning wheel and bag of marbles – events and probability
MathematicsProbabilityAges 12–13
Use it with your class: students open it from a link or a QR code, with no account needed.
Next in Probability
A spinning wheel is divided into colored slices of different widths (or a bag holds a matching number of marbles per color). Spin once or spin fast many times; a table and chart compare each color's experimental frequency with its probability, calculated as that color's slot count divided by the total. Change the slot ratios to see certain, impossible, and random events in action (a slot count of 0 gives an impossible event).
Lesson: Events; the probability of a random event in simple games
What it shows
When all outcomes are equally likely, the probability of an event is the number of favourable outcomes divided by the total number of outcomes. On the spinning wheel every slot is equally likely, so a color's probability is its number of slots divided by the total; a bag holding the same numbers of marbles gives the same probabilities. A color with 0 slots gives an impossible event, a color that has every slot gives a certain event, and anything in between is a random event. Many spins show the frequencies approaching these probabilities.
How to use
Set the Number of colors and type the Number of slots per color, separated by commas, for example 3,2,1,2, or click a slice to add a slot. Ask students to predict each color's probability, then press Spin once several times and Spin fast for a longer run. Compare the solid frequency bars with the probability markers in the chart. Switch the Model to Bag of marbles, and try setting one color to 0 slots.
Parameters you can change
- Number of colors 2–6
- Number of slots per color, separated by commas
- Number of spins for 'Spin fast' 10–500 spins
- Model Spinning wheel, Bag of marbles
Questions to explore
- With slots 3, 2, 1, 2, which color is most likely to come up, and what is its probability?
- How can you set up the wheel so that getting red is an impossible event? And a certain event?
- After 10 spins and after 500 spins, which frequencies are closer to the probabilities, and why?
