Copyright © University of Cambridge. All rights reserved.
Winning the Lottery
In a far-away land, the lottery consists of four balls numbered 1 to 4, which are placed in a bag.
To enter, you choose one number.
To win, your number must match the number that is drawn from the bag.
What is the chance of winning this lottery?
The people running the lottery in this far-away land decide that it is too easy to win. So, they change their lottery game.
In the new lottery, there are still four balls numbered 1 to 4, which are placed in a bag.
Now, to enter, you choose two numbers.
To win, your numbers must match (in any order) the two numbers that are drawn from the bag.
What is the chance of winning this new lottery?
Have the organisers made it harder to win compared with their original version?
Can you create your own version of the lottery which would also be harder to win than the first game?
How do you know that your game is harder?
Why do this problem?
This problem offers an engaging context for developing children's understanding of experimental and theoretical probability. Alongside experimental data, they can be encouraged to calculate theoretical probabilities by working systematicallly, and listing all possible winning combinations.
Possible approach
You could simulate the lottery yourself by having numbered balls or digit cards in a bag. You could pick out the 'winning' number yourself and record the results somewhere for all to see.
To begin with, you could set up the lottery with only four balls available and 'your ticket' has just one number. Explain the way this lottery works to the group and invite suggestions for the number to choose on your ticket. You could simulate a draw a few times.
Once the group has got a feel for this lottery, you could pose a few questions, such as:
What is the chance of winning our lottery?
How many times would you expect to win in ten draws?
How many times would you expect to win in twenty draws?
How many times would you expect to win in fifty draws?
How many times would you expect to win in one hundred draws?
Give children time to work on these questions in pairs, making it clear that you will be expecting them to explain their thinking.
After a suitable period, bring the whole class together to share their ideas and to ask them to justify their predictions mathematically. For example, some children might say that there are four possible winning numbers (1, 2, 3, or 4) and if you have chosen one of them on your ticket, the chance of you winning is 1 out of 4 or a quarter or 25%.
You could actually perform ten/twenty/fifty etc draws. Did the simulations match their predictions? This is a good chance to bring up the idea that the higher the number of draws, the more likely the experimental data will match the theoretical data (i.e. one in four).
You can encourage the group to investigate the modified version of the lottery in a similar way. This time, it is more of a challenge to list all the possible draws.
Key questions
What number/s could be drawn?
What are all the possible draws?
How do you know you have got them all?
How can you tell which version of the lottery is easier/harder to win?
Possible extension
Encouraging learners to find their own ways to make it more difficult to win the lottery is a never-ending task! You may be surprised to observe those who stick to situations which they feel comfortable analysing and those who push themselves a bit further.
Possible support
It will be helpful for learners to have access to physical resources in their pairs, such as numbered balls or digit cards.