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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.

\( \times 2\)

\(+5\)

\(37\)


Sydney says:
'I think of a number. I double my number and add 5 the answer is 37'
What number was Sydney first thinking of?

Working:

Correct Wrong


Julia says:
'I am also thinking of a number. If I multiply my number by 2 and add 6 the answer is 44'
What number was Julia first thinking of?

Working:

Correct Wrong
Destiny says:
'I think of a number. I multiply my number by 3 and add 3 the answer is 33'
What number was Destiny first thinking of?

Working:

Correct Wrong
Morgan says:
'Can you guess what number I am thinking of if when I multiply it by 3 and add 2 the answer is 17?'
What number was Morgan first thinking of?

Working:

Correct Wrong
Kaitlyn says:
'If I divide my number by 5 and add 5 the answer is 12'
What number was Kaitlyn first thinking of?

Working:

Correct Wrong
Savannah says:
'If I multiply my number by 3 then add 5 then add 4 then add 3 the answer is 30'
What number was Savannah first thinking of?

Working:

Correct Wrong
Katherine says:
'I am thinking of my favourite number. If I add 4 to my number then divide the result by 2, the answer is 18'
What number was Katherine first thinking of?

Working:

Correct Wrong
Alexandra says:
'My plan was to add 3 to my number then multiply the result by 5. Then I multiplied the result by 2 and finally subtracted 6. The answer is 144'
What number was Alexandra first thinking of?

Working:

Correct Wrong
Rachel says:
'I decided to add 4 to my number then multiply the result by 3, After that I subtracted 2 then doubled the result. The answer is 44'
What number was Rachel first thinking of?

Working:

Correct Wrong
Lily says:
'If I multiply my number by 5 and subtract 2 then multiply the result by 5, the answer is 6 less than 146'
What number was Lily 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 11 January 'Starter of the Day' page by S Johnson, The King John School:

"We recently had an afternoon on accelerated learning.This linked really well and prompted a discussion about learning styles and short term memory."

Comment recorded on the 1 May 'Starter of the Day' page by Phil Anthony, Head of Maths, Stourport High School:

"What a brilliant website. We have just started to use the 'starter-of-the-day' in our yr9 lessons to try them out before we change from a high school to a secondary school in September. This is one of the best resources on-line we have found. The kids and staff love it. Well done an thank you very much for making my maths lessons more interesting and fun."

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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:

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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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