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

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\( \times 2\) \(+3.8\) \(6.8\) David says: 'I think of a number. I double my number and add 3.8 the answer is 6.8' What number was David first thinking of?	Working:
Nicholas says: 'I am also thinking of a number. If I multiply my number by 2 and add 9.6 the answer is 25.4' What number was Nicholas first thinking of?	Working:
James says: 'I think of a number. I multiply my number by 3 and add 5.7 the answer is 12.9' What number was James first thinking of?	Working:
John says: 'Can you guess what number I am thinking of if when I multiply it by 1.4 and add 3.5 the answer is 5.88?' What number was John first thinking of?	Working:
Jonathan says: 'If I divide my number by 5 and add 4.4 the answer is 5.36' What number was Jonathan first thinking of?	Working:
Samuel says: 'If I multiply my number by 6.5 then add 3.3 then add 6.7 then add 8 the answer is 75.2' What number was Samuel first thinking of?	Working:
Christian says: 'I am thinking of my favourite number. If I add 10 to my number then divide the result by 2, the answer is 9.6' What number was Christian first thinking of?	Working:
Noah says: 'My plan was to add 9.3 to my number then multiply the result by 9.2. Then I multiplied the result by 9.6 and finally subtracted 5.2. The answer is 1425.584' What number was Noah first thinking of?	Working:
Dylan says: 'I decided to add 5.4 to my number then multiply the result by 3, After that I subtracted 3.4 then doubled the result. The answer is 84.4' What number was Dylan first thinking of?	Working:
Benjamin says: 'If I multiply my number by 1.7 and subtract 6.5 then multiply the result by 6.8, the answer is 7.9 less than 9.94' What number was Benjamin 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

23 or Bust

Answers

Go Maths

Maths Map

Teachers

Description of Levels

Curriculum Reference

Example

Method 1 - Work backwards

Method 2 - Form and solve an equation