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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\( \times 2\) \(+4\) \(20\) Dominic says: 'I think of a number. I double my number and add 4 the answer is 20' What number was Dominic first thinking of?	Working:
Sebastian says: 'I am also thinking of a number. If I multiply my number by 2 and add 3 the answer is 31' What number was Sebastian first thinking of?	Working:
Xavier says: 'I think of a number. I multiply my number by 3 and add 6 the answer is 51' What number was Xavier first thinking of?	Working:
Jaden says: 'Can you guess what number I am thinking of if when I multiply it by 5 and add 2 the answer is 37?' What number was Jaden first thinking of?	Working:
Jesse says: 'If I divide my number by 5 and add 2 the answer is 18' What number was Jesse first thinking of?	Working:
Devin says: 'If I multiply my number by 3 then add 5 then add 6 then add 4 the answer is 72' What number was Devin first thinking of?	Working:
Seth says: 'I am thinking of my favourite number. If I add 8 to my number then divide the result by 2, the answer is 14' What number was Seth first thinking of?	Working:
Antonio says: 'My plan was to add 5 to my number then multiply the result by 2. Then I multiplied the result by 4 and finally subtracted 6. The answer is 58' What number was Antonio first thinking of?	Working:
Richard says: 'I decided to add 6 to my number then multiply the result by 3, After that I subtracted 2 then doubled the result. The answer is 122' What number was Richard first thinking of?	Working:
Miquel says: 'If I multiply my number by 3 and subtract 3 then multiply the result by 5, the answer is 3 less than 33' What number was Miquel 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