Probability: the lucky-draw bag at the school mela
Fill a lucky-draw bag with coloured balls, place the chance of winning on a scale from impossible to certain, and draw many times to test it.
Core concept
Probability = favourable outcomes ÷ all equally likely outcomes, and the share seen in many trials gets close to it
Topic: Probability
At the school mela, a student draws one ball from a bag without looking, and a red ball wins a prize. Every ball is equally likely to come out, so the probability: How likely something is to happen, from 0 (impossible) to 1 (certain). All key words of red is the number of red balls ÷ the number of balls. Probability goes from 0 (impossible) to 1 (certain); ½ is an even chance. The theory says what should happen on average: Add all the values and divide by how many there are. Also called the mean. All key words. If we draw many times, putting the ball back each time, the share of reds we get is the experimental probability, and with more draws it usually comes closer to the theory.
What you will learn
- Find the probability of an event as favourable outcomes ÷ all outcomes.
- Place probabilities on a scale from impossible to certain.
- Compare experimental and theoretical probability, and see the effect of more trials.
Before you start
- Write a fraction and change it to a decimal.
Materials
- A cloth bag and coloured balls (or bottle caps)
Equipment
- A tally sheet
Procedure
- Tap + on a colour to put a ball into the bag; tap a ball in the bag to take it out.
- Watch the red arrow on the chance scale.
- Make winning impossible, then certain, then an even chance, and record each.
- Make the chance of red exactly 1/4, change the draws to 1000, and compare the share of reds with the theory.
How this simulation is simplified
- Every ball is equally likely to be drawn, and it is put back after each draw.