Faulty Button

A Maths Starter Of The Day

One of the keys on a calculator is faulty. When you press it you get a different number. Some of the results produced by the calculator are shown below. Which is the faulty key?

1

5

5

+

5

2

2

=

677

3

7

6

-

1

7

2

=

204

2

4

7

+

3

8

7

=

624

9

4

3

-

2

3

2

=

711

4

1

7

+

1

2

6

=

538

Topics: Starter | Arithmetic | Calculator | Problem Solving

  • Transum,
  •  
  • One strategy would be to jot down the digits 0 to 9 on some scrap paper of the back of the exercise book. Next cross out the digits used in the correct calculations as those buttons could not be faulty… Or could they? For example if 7 was the faulty key and always produced a 5 instead of a 7, the calculation 237 – 117 would still produce the correct answer of 120. Did your pupils come up with a better strategy?

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Previous Day | This starter is for 11 February | Next Day

 

Answers

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Note to teacher: Doing this activity once with a class helps students develop strategies. It is only when they do this activity a second time that they will have the opportunity to practise those strategies. That is when the learning is consolidated. Click the button above to regenerate another version of this starter from random numbers.



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Laptops In Lessons

Teacher, do your students have access to computers such as tablets, iPads or Laptops?  This page was really designed for projection on a whiteboard but if you really want the students to have access to it here is a concise URL for a version of this page without the comments:

Transum.org/go/?Start=February11

However it would be better to assign one of the student interactive activities below.

Laptops In Lessons

Here is the URL which will take them to a related student activity.

Transum.org/go/?to=six

Student Activity

If you think faulty calculators still have a use try this.

Transum.org/go/?to=broken

Student Activity

 


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