# 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 2: Decimal THOAN problems. You can earn a trophy if you get at least 7 questions correct.

 $$\times 2$$$$+4.2$$$$14.6$$Benjamin says:'I think of a number. I double my number and add 4.2 the answer is 14.6'What number was Benjamin first thinking of? Working: Logan says:'I am also thinking of a number. If I multiply my number by 2 and add 7.1 the answer is 12.9'What number was Logan first thinking of? Working: Zachary says:'I think of a number. I multiply my number by 3 and add 5.5 the answer is 29.2'What number was Zachary first thinking of? Working: Jose says:'Can you guess what number I am thinking of if when I multiply it by 6.8 and add 7.8 the answer is 38.4?'What number was Jose first thinking of? Working: Elijah says:'If I divide my number by 5 and add 6.6 the answer is 7.18'What number was Elijah first thinking of? Working: Angel says:'If I multiply my number by 6.2 then add 2.7 then add 4.6 then add 8.2 the answer is 71.92'What number was Angel first thinking of? Working: Kevin says:'I am thinking of my favourite number. If I add 7.2 to my number then divide the result by 2, the answer is 8.2'What number was Kevin first thinking of? Working: Jack says:'My plan was to add 5.3 to my number then multiply the result by 6.3. Then I multiplied the result by 9.9 and finally subtracted 2.5. The answer is 758.414'What number was Jack first thinking of? Working: Caleb says:'I decided to add 4 to my number then multiply the result by 3, After that I subtracted 8.4 then doubled the result. The answer is 39'What number was Caleb first thinking of? Working: Justin says:'If I multiply my number by 5.3 and subtract 3 then multiply the result by 4.5, the answer is 8.6 less than 66.65'What number was Justin first thinking of? Working:
Check

This is Think of a Number level 2. You can also try:
Level 1 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 9 April 'Starter of the Day' page by Jan, South Canterbury:

"Thank you for sharing such a great resource. I was about to try and get together a bank of starters but time is always required elsewhere, so thank you."

Comment recorded on the 2 May 'Starter of the Day' page by Angela Lowry, :

"I think these are great! So useful and handy, the children love them.
Could we have some on angles too please?"

#### ChrisMaths

Christmas activities make those December Maths lessons interesting, exciting and relevant. If students have access to computers there are some online activities to keep them engaged such as Christmas Ornaments and Christmas Light Up.

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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.

## Maths Map

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## 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.

## 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.

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