# 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 1Level 2Level 3DescriptionHelpAlgebra

This is level 3: Negative decimal THOAN problems. You can earn a trophy if you get at least 7 questions correct.

 $$\times 2$$$$+25$$$$9$$Riley says:'I think of a number. I double my number and add 25 the answer is 9'What number was Riley first thinking of? Working: Haley says:'I am also thinking of a number. If I multiply my number by 2 and add 9.3 the answer is 4.9'What number was Haley first thinking of? Working: Gabrielle says:'I think of a number. I multiply my number by 3 and add 2.5 the answer is -25.7'What number was Gabrielle first thinking of? Working: Nicole says:'Can you guess what number I am thinking of if when I multiply it by 5.4 and add 1.1 the answer is -49.12?'What number was Nicole first thinking of? Working: Kylie says:'If I divide my number by 5 and add 5.8 the answer is 3.96'What number was Kylie first thinking of? Working: Katelyn says:'If I multiply my number by 9.3 then add 2 then add 3.5 then add 4.1 the answer is -1.56'What number was Katelyn first thinking of? Working: Zoe says:'I am thinking of my favourite number. If I add 14 to my number then divide the result by 2, the answer is 4.7'What number was Zoe first thinking of? Working: Paige says:'My plan was to add 4.2 to my number then multiply the result by 3.4. Then I multiplied the result by 7.2 and finally subtracted 1.9. The answer is -121.852'What number was Paige first thinking of? Working: Gabriella says:'I decided to add 1.2 to my number then multiply the result by 3, After that I subtracted 7.2 then doubled the result. The answer is -30.6'What number was Gabriella first thinking of? Working: Jenna says:'If I multiply my number by 6.6 and subtract 5.8 then multiply the result by 7.4, the answer is 2.5 less than -372.532'What number was Jenna first thinking of? Working:
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This is Think of a Number level 3. You can also try:
Level 1 Level 2

## 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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#### 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?

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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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## 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.

## 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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