# How do you do it?

This group activity will encourage you to share calculation strategies and to think about which strategy might be the most efficient.

## Problem

This problem is designed to be done in a group. So, ideally, you need to find three or four other people to work with you.

Firstly, take some time to work on your own to find the answers to these calculations, without writing anything down. (Although it would be good to write down the answer itself so you don't forget it.)

$19 \times 24$

$198 + 997$

Half of $57.6$

$3841 - 665.3$

$5.2 \div 4$

$101 \times 16 \times 4$

Now, join together with the other people in your group and focus on the first question.

Do you all agree on the answer?

Give EVERYONE in the group time to explain how they worked it out.

As a group, decide whose method you think is most efficient and why.

Do the same for each of the six questions: give everyone the chance to explain their own method and then choose the most efficient for that calculation.

For the final bit of the challenge, you will need a set of these cards - one set for the group. Each card has another calculation on it.

As a group, decide on the most efficient method for each of the cards.

What did you decide and why?

## Getting Started

Can you round the numbers up or down to help?

Can you 'picture' the calculation in your head somehow?

Perhaps you can use some number facts that you know well to help?

Does your answer sound reasonable?

## Student Solutions

This problem encouraged you to work as a group, discussing and sharing different calculation strategies. There may be several different ways of working out the answer to a particular calculation; some are more efficient than others. Can you find different ways of working out the answer to the questions? Look at different types of questions, such as the ones given in the problem. Are the same methods always the most efficient?

William and Conner from St Patrick's R.C. Primary School submitted their solution:

William and Conner tackled these problems by splitting the numbers into more familiar-and easier to handle- numbers. They then dealt with these separately and combined the answers.

Ben, Aeron, Isla and Emily School from St Mary Redcliffe Primary explained how they worked out their answers to the calculations on the cards:

The Maths Group at St Teresa's in Surrey had some slightly different methods:

Very well done. I wonder which method you prefer in each case? Or perhaps you have a method that you think works even better for you?

## Teachers' Resources

### Why do this problem?

### Possible approach

$19 \times 24$

$198 + 997$

Half of $57.6$

$3841 - 665.3$

$5.2 \div 4$

$101 \times 16 \times 4$

Next introduce learners to the group task. Ask them to consider the first calculation and compare answers. It is very possible that they won't agree but in many ways this is a good thing! Explain to them that you would like them to decide what the right answer is by sharing the ways they worked it out. Emphasise that you would like *everyone* in the group to have a turn at explaining their own method. Once the group has decided on the answer, the second part of the task is to decide which method they think is most efficient. They can then repeat this process for each of the above calculations.

Once the group has completed this, give them a set of these cards. The challenge now is to work out the answers to this new set of calculations, but working together. The questions on the cards are similar in some ways to the questions initially given, so the idea would be for children to notice the similarities. Encourage them, therefore, to use a method that they have identified as efficient in the first part of the task. It would be good to give each group an A3 sheet of paper (or even bigger) to record the methods that they choose for the calculations on the cards. The posters they create can form the basis of a whole-class discussion in the plenary, comparing their chosen methods, and will make an informative display.

### Key questions

*everyone*in the group explained their method?

### Possible extension

### Possible support