Think of a Number

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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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John 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 John first thinking of?	Working:
Jonathan 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 Jonathan first thinking of?	Working:
Samuel 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 Samuel first thinking of?	Working:
Christian 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 Christian first thinking of?	Working:
Noah 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 Noah first thinking of?	Working:
Dylan 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 Dylan first thinking of?	Working:
Benjamin 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 Benjamin first thinking of?	Working:
Logan 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 Logan first thinking of?	Working:
Zachary 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 Zachary first thinking of?	Working:
Jose 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 Jose 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

Snooker Angles

Answers

Go Maths

Maths Map

Teachers

Description of Levels

Curriculum Reference

Example

Method 1 - Work backwards

Method 2 - Form and solve an equation