Think of a Number

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Featured Activity Lemon Law A fascinating digit changing challenge. Change the numbers on the apples so that the number on the lemon is the given total. Can you figure out, by understanding place value, how this works?	Answers There are answers to this exercise but they are available in this space to teachers, tutors and parents who have logged in to their Transum subscription on this computer. A Transum subscription unlocks the answers to the online exercises, quizzes and puzzles. It also provides the teacher with access to quality external links on each of the Transum Topic pages and the facility to add to the collection themselves. Subscribers can manage class lists, lesson plans and assessment data in the Class Admin application and have access to reports of the Transum Trophies earned by class members. If you would like to enjoy ad-free access to the thousands of Transum resources, receive our monthly newsletter, unlock the printable worksheets and see our Maths Lesson Finishers then sign up for a subscription now: Subscribe
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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.

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Amelia once said: 'I think of a number. I multiply it by 3, add 9, divide by 2, and then subtract 6. The result is the same number that I started with.' What number was Amelia first thinking of?	Working:
Mariah says: 'I think of a number. I multiply it by 4, subtract 16, divide by 2, and then add 6. The result is the same number that I started with.' What number was Mariah first thinking of?	Working:
Jordan says: 'I think of a number. I add 5, multiply the result by 2, subtract 6, and then divide by 2. The result is twice the number that I started with.' What number was Jordan first thinking of?	Working:
Jocelyn says: 'I think of a number. I triple it, add 9, divide by 3, and then subtract 4. The result is half the number that I started with.' What number was Jocelyn first thinking of?	Working:
Arianna says: 'I think of a number. I multiply it by 2, add 6, divide by 3, and then subtract 1. The result is half the number that I started with.' What number was Arianna first thinking of?	Working:
Isabel says: 'I think of a number. I subtract 2, multiply the result by 4, add 8, and then divide by 2. The result is three times the number that I started with.' What number was Isabel first thinking of?	Working:
Marissa says: 'I think of a number. I add 3, multiply by 2, subtract 4, and then divide by 5. The result is twice the number that I started with.' What number was Marissa first thinking of?	Working:
Autumn says: 'I think of a number. I multiply it by 4, add 8, divide by 3, and then subtract 6. The result is the same number that I started with.' What number was Autumn first thinking of?	Working:
Melanie says: 'I think of a number and subtract it from 22. The result I divide by double the number. Finally I add 5 and find the result is 10.' What number was Melanie first thinking of?	Working:
Aaliyah says: 'I think of a number. I subtract three lots of that number from 100 then I add two and a half. The result I get is double my original number plus 50.' What number was Aaliyah first thinking of?	Working:

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.

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Instructions

More Activities:

Featured Activity

Lemon Law

Answers

Go Maths

Maths Map

Teachers

Description of Levels

Curriculum Reference

Example

Method 1 - Work backwards

Method 2 - Form and solve an equation