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Marbles in a bag
Different colours, different quantities. Draw one and watch the odds change.
Made by the PaperCarnival team · Updated
4 in the bag
| Colour | In the bag | Chance |
|---|---|---|
| Red | 3/4 | 75% |
| Blue | 1/4 | 25% |
What is in the bag
4 marbles in the bag when it is full.
After a draw
The marble stays out, so the odds change after every draw.
Draw several at once
The odds table
The chance of each colour is on the stage as a fraction and a percentage, before every draw.
Without replacement the fractions change after every draw, which is the whole lesson: the second draw is not the same experiment as the first.
Sound
A marble makes a clack as it comes out. The colour is always on screen as a word as well as a colour.
The oldest probability lesson there is
Three red and one blue is where every probability lesson starts, because everybody can see the answer before they can write it down. Three out of four. Seventy-five percent. The bag on this page shows both forms at once, next to the marbles themselves, so the fraction and the percentage and the handful of counters are visibly the same fact.
You can hide the table when the point is for the class to work it out, and put it back the moment somebody wants to check. Nothing is timed and nothing is scored: it is a bag, and it does what a bag does.
Drawing several at once is how a class watches a run settle towards the odds on the table: ten marbles a press, with the results stacked up beside the bag. For a bag where nothing comes back, the bag of tokens does the same job with your own words instead of colours.
Kept in this browser under pph.marbles.bag, pph.marbles.replace, pph.marbles.count, pph.marbles.odds and pph.marbles.muted, and nowhere else. Accounts, printing, storage and what the page loads are answered on the FAQ.
Questions
- Is the draw truly random?
- Yes. Each marble is picked with the browser's cryptographic random number generator, weighted by how many of each colour are actually in the bag, and it is picked before the bag shakes.
- What is the difference between the two modes?
- Without replacement the marble stays out, so the bag empties and the odds change after every draw. With replacement it goes back in, so every draw is the same experiment and the bag never runs out.
- Can I hide the odds from the class?
- Yes. Turn the odds table off in the Odds tab and the stage shows only the bag and the result, which is what you want when the class is meant to work the fractions out for themselves.
- Can I use it for a raffle?
- You can use it to draw a colour, but there are no stakes here and it is not built for prizes of value. It is a probability demonstration and a party picker.
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