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Think of a Number

Ten students think of a number then perform various operations on that number. You have to find what the original numbers were.

Level 1 Level 2 Level 3 Description Help Algebra

This is level 1: Whole number THOAN problems. You can earn a trophy if you get at least 7 questions correct.

\( \times 2\)

\(+6\)

\(10\)


Samantha says:
'I think of a number. I double my number and add 6 the answer is 10'
What number was Samantha first thinking of?

Working:

Correct Wrong


Ava says:
'I am also thinking of a number. If I multiply my number by 2 and add 4 the answer is 18'
What number was Ava first thinking of?

Working:

Correct Wrong
Ashley says:
'I think of a number. I multiply my number by 3 and add 3 the answer is 9'
What number was Ashley first thinking of?

Working:

Correct Wrong
Sophia says:
'Can you guess what number I am thinking of if when I multiply it by 6 and add 3 the answer is 129?'
What number was Sophia first thinking of?

Working:

Correct Wrong
Elizabeth says:
'If I divide my number by 5 and add 2 the answer is 18'
What number was Elizabeth first thinking of?

Working:

Correct Wrong
Alexis says:
'If I multiply my number by 4 then add 2 then add 5 then add 3 the answer is 34'
What number was Alexis first thinking of?

Working:

Correct Wrong
Grace says:
'I am thinking of my favourite number. If I add 4 to my number then divide the result by 2, the answer is 5'
What number was Grace first thinking of?

Working:

Correct Wrong
Sarah says:
'My plan was to add 3 to my number then multiply the result by 2. Then I multiplied the result by 3 and finally subtracted 3. The answer is 99'
What number was Sarah first thinking of?

Working:

Correct Wrong
Alyssa says:
'I decided to add 5 to my number then multiply the result by 3, After that I subtracted 3 then doubled the result. The answer is 102'
What number was Alyssa first thinking of?

Working:

Correct Wrong
Mia says:
'If I multiply my number by 5 and subtract 4 then multiply the result by 2, the answer is 5 less than 137'
What number was Mia first thinking of?

Working:

Correct Wrong
Check

This is Think of a Number level 1. You can also try:
Level 2 Level 3

Instructions

Try your best to answer the questions above. Type your answers into the boxes provided leaving no spaces. As you work through the exercise regularly click the "check" button. If you have any wrong answers, do your best to do corrections but if there is anything you don't understand, please ask your teacher for help.

When you have got all of the questions correct you may want to print out this page and paste it into your exercise book. If you keep your work in an ePortfolio you could take a screen shot of your answers and paste that into your Maths file.

Transum.org

This web site contains over a thousand free mathematical activities for teachers and pupils. Click here to go to the main page which links to all of the resources available.

Please contact me if you have any suggestions or questions.

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Mathematicians are not the people who find Maths easy; they are the people who enjoy how mystifying, puzzling and hard it is. Are you a mathematician?

Comment recorded on the 1 August 'Starter of the Day' page by Peter Wright, St Joseph's College:

"Love using the Starter of the Day activities to get the students into Maths mode at the beginning of a lesson. Lots of interesting discussions and questions have arisen out of the activities.
Thanks for such a great resource!"

Comment recorded on the 28 May 'Starter of the Day' page by L Smith, Colwyn Bay:

"An absolutely brilliant resource. Only recently been discovered but is used daily with all my classes. It is particularly useful when things can be saved for further use. Thank you!"

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Are you looking for something specific? An exercise to supplement the topic you are studying at school at the moment perhaps. Navigate using our Maths Map to find exercises, puzzles and Maths lesson starters grouped by topic.

Teachers

If you found this activity useful don't forget to record it in your scheme of work or learning management system. The short URL, ready to be copied and pasted, is as follows:

Do you have any comments? It is always useful to receive feedback and helps make this free resource even more useful for those learning Mathematics anywhere in the world. Click here to enter your comments.

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Description of Levels

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Level 1 - Whole number THOAN problems

Level 2 - Decimal THOAN problems

Level 3 - Negative decimal THOAN problems

Answers to this exercise are available lower down this page when you are logged in to your Transum account. If you don’t yet have a Transum subscription one can be very quickly set up if you are a teacher, tutor or parent.

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Example

Daniel says 'If I double my number and add 6 the answer is 30'

Method 1 - Work backwards

Start at the end of the sentence with the answer 30 and undo all of the operations Daniel performed on his number in reverse order.

30 minus 6 then divide by two

The number Daniel was thinking about was 12

 

Method 2 - Form and solve an equation

Let the number that Daniel is first thinking of be n.

2n + 6 = 30

Subtract 6 from both sides

2n = 24

Divide both sides by 2

n = 12

The number Daniel was thinking about was 12

 

Don't wait until you have finished the exercise before you click on the 'Check' button. Click it often as you work through the questions to see if you are answering them correctly. You can double-click the 'Check' button to make it float at the bottom of your screen.

Answers to this exercise are available lower down this page when you are logged in to your Transum account. If you don’t yet have a Transum subscription one can be very quickly set up if you are a teacher, tutor or parent.

Log in Sign up

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