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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.

\( \times 2\)

\(+2\)

\(42\)


Cole says:
'I think of a number. I double my number and add 2 the answer is 42'
What number was Cole first thinking of?

Working:

Correct Wrong


Brayden says:
'I am also thinking of a number. If I multiply my number by 2 and add 5 the answer is 41'
What number was Brayden first thinking of?

Working:

Correct Wrong
Wyatt says:
'I think of a number. I multiply my number by 3 and add 2 the answer is 11'
What number was Wyatt first thinking of?

Working:

Correct Wrong
Chase says:
'Can you guess what number I am thinking of if when I multiply it by 4 and add 2 the answer is 22?'
What number was Chase first thinking of?

Working:

Correct Wrong
Steven says:
'If I divide my number by 5 and add 4 the answer is 10'
What number was Steven first thinking of?

Working:

Correct Wrong
Timothy says:
'If I multiply my number by 4 then add 3 then add 4 then add 4 the answer is 87'
What number was Timothy first thinking of?

Working:

Correct Wrong
Dominic says:
'I am thinking of my favourite number. If I add 12 to my number then divide the result by 2, the answer is 26'
What number was Dominic first thinking of?

Working:

Correct Wrong
Sebastian says:
'My plan was to add 3 to my number then multiply the result by 2. Then I multiplied the result by 2 and finally subtracted 3. The answer is 29'
What number was Sebastian first thinking of?

Working:

Correct Wrong
Xavier says:
'I decided to add 5 to my number then multiply the result by 3, After that I subtracted 4 then doubled the result. The answer is 76'
What number was Xavier first thinking of?

Working:

Correct Wrong
Jaden says:
'If I multiply my number by 6 and subtract 5 then multiply the result by 2, the answer is 6 less than 20'
What number was Jaden 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 14 September 'Starter of the Day' page by Trish Bailey, Kingstone School:

"This is a great memory aid which could be used for formulae or key facts etc - in any subject area. The PICTURE is such an aid to remembering where each number or group of numbers is - my pupils love it!
Thanks"

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Go Maths

Learning and understanding Mathematics, at every level, requires learner engagement. Mathematics is not a spectator sport. Sometimes traditional teaching fails to actively involve students. One way to address the problem is through the use of interactive activities and this web site provides many of those. The Go Maths page is an alphabetical list of free activities designed for students in Secondary/High school.

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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:

Alternatively, if you use Google Classroom, all you have to do is click on the green icon below in order to add this activity to one of your classes.

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When planning to use technology in your lesson always have a plan B!

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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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