Reach the target with calculators

Intention
This activity can be used either as a whole class or paired activity in the main part of the lesson, or, more briefly, during the plenary session.

Outcomes
Children develop calculator skills by beginning to select the correct key sequence to carry out calculations involving more than one step.

NNS references

Year 5 

Calculation

Understanding multiplication and division

Using a calculator

Year 6 

Calculation

Understanding multiplication and division

Using a calculator

Resources

Whole class activity

2 sets of digit cards 1-10
1 card each with the following numbers 25, 50, 75, 100
A random number generator.
An overhead projector, overhead calculator and class set of calculators.
Activity sheet and pencils

Paired work

2 sets of digit cards 1-10
1 card each with the following numbers 25, 50, 75, 100
Dice.
Two calculators
Activity sheets and pencils for each pair.


Activity

Quite often it is necessary to use the distributive law to solve these problems.
Set out the four large number cards face down on a table or fix to the board.
Set out the remaining cards in three or four rows beneath.
These will be used later.
Teachers should model the task first.

Begin by writing the number 436 on the board.
Underneath write the numbers: 100 8 6 4 1 9

Explain that the object is to make the number 436 using only the numbers on the board and that they can only use them once each.
Ask if anyone has an idea how to do it.
(One solution is (100 + 9) x 4)

Now generate a three-digit number using the random number generator.
Write the target number on the board.
Ask a pupil to choose 6 cards.
Turn these cards over and fix to the board.
The children, working in pairs, must use the four operations and any or all of the numbers once only to get as close to the target number as possible.
Tell the children to write down their calculations.
Give the children a time limit this will depend upon their age and experience.
At the end of the time ask if anyone reached the target. If so ask for a volunteer to come and demonstrate the solution using the overhead calculator. Ask if anyone did it another way.
If no one reached the target ask the child whose answer was closest to demonstrate.
If playing in pairs children can award themselves points:
10 points if they calculate the number exactly.
7 points if they are within 5 of the target.
5 points if they are within 10 of the target.

Observations, intervention and questions to ask

Can children use the distributive law?
Are children demonstrating flexibility and confidence with numbers; e.g. if they have the digit cards 2, 5, 4,1, 7 can they make 10 in more than one way?
Are children using the inverse operations to estimate? Using the example above 436/4 = 109. How can I make 109 using the numbers I have?
What do you need to multiply this by?
How can you make that from these numbers?
Could you add/subtract before you multiply/divide?
Which numbers did you find hardest?
Which big number was the hardest to work with? (75)
Which big number was the easiest to work with? (100)
Which numbers did you find easiest to calculate? (Evens multiples of 5, 10 25?) 
How could you use the calculator's memory to help?

What learning has taken place?

Children understand and use the distributive law.
Children begin to use the memory/brackets function.

Target  Numbers Calculation Points
       
       
       
       
       
Total  

 

1 2 3 4
5 6 7 8
9 10 25 50
75 100 1 2
3 4 5 6
7 8 9 10