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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.

\( \times 2\)

\(+5\)

\(23\)


Joshua says:
'I think of a number. I double my number and add 5 the answer is 23'
What number was Joshua first thinking of?

Working:

Correct Wrong


Matthew says:
'I am also thinking of a number. If I multiply my number by 2 and add 3 the answer is 45'
What number was Matthew first thinking of?

Working:

Correct Wrong
Ethan says:
'I think of a number. I multiply my number by 3 and add 2 the answer is 44'
What number was Ethan first thinking of?

Working:

Correct Wrong
Andrew says:
'Can you guess what number I am thinking of if when I multiply it by 2 and add 4 the answer is 12?'
What number was Andrew first thinking of?

Working:

Correct Wrong
Daniel says:
'If I divide my number by 5 and add 4 the answer is 18'
What number was Daniel first thinking of?

Working:

Correct Wrong
Christopher says:
'If I multiply my number by 5 then add 3 then add 4 then add 4 the answer is 81'
What number was Christopher first thinking of?

Working:

Correct Wrong
Joseph says:
'I am thinking of my favourite number. If I add 12 to my number then divide the result by 2, the answer is 11'
What number was Joseph first thinking of?

Working:

Correct Wrong
William says:
'My plan was to add 3 to my number then multiply the result by 4. Then I multiplied the result by 4 and finally subtracted 5. The answer is 283'
What number was William first thinking of?

Working:

Correct Wrong
David 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 138'
What number was David first thinking of?

Working:

Correct Wrong
Nicholas says:
'If I multiply my number by 4 and subtract 6 then multiply the result by 3, the answer is 3 less than 21'
What number was Nicholas 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.

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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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