Teacher guidance

You may wish to show the task on a whiteboard and talk about the concept of descendants

• In this task, there is a photograph of a girl, about your age, who lived 110 years ago. She grew up, had children, who had their own children and so on.
• A family party is being planned for all her descendants. Your task is to make a good estimate of how many descendants you might expect her to have.
• You are given some facts – think about why there are there, and use them!
• Show your working so I can know what you did and how you reached your answer.

The task requires multiplicative calculations to represent changes over time.

The following probing questions may be helpful:

• What assumptions have you made?
• When you are thinking about all her descendants over the 110 years, are there any other factors you need to consider?
• Have you made sure you have thought of all her descendants?

There are several assumptions needed for the task:

• How many children the girl had and when.
• The average age of giving birth and whether this changes over time.
• When and how, during the 20th century, the birth rate changed.
• The proportion of her descendants that conformed to the average birth rates.
• At what age people die, and so how many descendants are still alive for the party.

Note: If pupils use more than 25 years between generations, they are likely to work with only 3 generations so may consider just counting. If so, they should be encouraged to consider a smaller number of years between generations.