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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.

\( \times 2\)

\(+2\)

\(44\)


Maya says:
'I think of a number. I double my number and add 2 the answer is 44'
What number was Maya first thinking of?

Working:

Correct Wrong


Mary says:
'I am also thinking of a number. If I multiply my number by 2 and add 3 the answer is 15'
What number was Mary first thinking of?

Working:

Correct Wrong
Michelle says:
'I think of a number. I multiply my number by 3 and add 5 the answer is 23'
What number was Michelle first thinking of?

Working:

Correct Wrong
Jada says:
'Can you guess what number I am thinking of if when I multiply it by 5 and add 6 the answer is 81?'
What number was Jada first thinking of?

Working:

Correct Wrong
Sara says:
'If I divide my number by 5 and add 5 the answer is 26'
What number was Sara first thinking of?

Working:

Correct Wrong
Audrey says:
'If I multiply my number by 4 then add 2 then add 3 then add 5 the answer is 70'
What number was Audrey first thinking of?

Working:

Correct Wrong
Brooklyn says:
'I am thinking of my favourite number. If I add 10 to my number then divide the result by 2, the answer is 22'
What number was Brooklyn first thinking of?

Working:

Correct Wrong
Vanessa says:
'My plan was to add 2 to my number then multiply the result by 3. Then I multiplied the result by 4 and finally subtracted 5. The answer is 175'
What number was Vanessa first thinking of?

Working:

Correct Wrong
Amanda says:
'I decided to add 6 to my number then multiply the result by 3, After that I subtracted 3 then doubled the result. The answer is 42'
What number was Amanda first thinking of?

Working:

Correct Wrong
Ariana says:
'If I multiply my number by 4 and subtract 3 then multiply the result by 6, the answer is 5 less than 83'
What number was Ariana 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.

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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 26 March 'Starter of the Day' page by Julie Reakes, The English College, Dubai:

"It's great to have a starter that's timed and focuses the attention of everyone fully. I told them in advance I would do 10 then record their percentages."

Comment recorded on the 25 June 'Starter of the Day' page by Inger.kisby@herts and essex.herts.sch.uk, :

"We all love your starters. It is so good to have such a collection. We use them for all age groups and abilities. Have particularly enjoyed KIM's game, as we have not used that for Mathematics before. Keep up the good work and thank you very much
Best wishes from Inger Kisby"

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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:

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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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