Think of a number

1
Mind reading
Think of a number
Multiply it by 2
Add 8
Divide by 2
Subtract the number you started with
What is your answer?
2
Mind reading
4
3
Mind reading
Think of a number
Add 3
Double it
Subtract the number you first thought of
Subtract it again
What is your answer?
4
Mind reading
6
5
Mind reading
Everybody started with different numbers, but
ended up with the same number. Why?
The number you first thought of is always
eventually subtracted.
Everyone has performed the same operations so you
all end up with the same answer.
6
Mind reading
Think of a number
n
7
Mind reading
Multiply it by 3
3n
8
Mind reading
Add 14
3n 14
9
Mind reading
Subtract the number you first thought of
2n 14
10
Mind reading
Divide by 2
n 7
11
Mind reading
Subtract the number you first thought of
7
12
Expressions
An expression consists of one or more terms.
3n is an expression.
3n 8 is an expression with two terms.
13
Think of a Number

• Double it
• Add 3
• Multiply by 4
• Subtract 12
• Divide by 8.

14
Think of a Number

• Double it
• Add 20
• Subtract original number
• Subtract 5
• Subtract original number.

15
Think of a Number

• Add 4
• Subtract 3
• Add 9
• Subtract original number.

16
Think of a Number

• Add 8
• Double it
• Subtract original number
• Subtract 1
• Subtract original number.

17
Think of a Number

• Add 3
• Double it
• Subtract original number
• Add 1
• Subtract original number.

18
Think of a Number

• Add 2
• Treble it
• Subtract original number
• Halve it
• Subtract original number
• Add 4.

19

• Think of a number
• Double it
• Add 3
• Multiply by 4
• Subtract 12
• Divide by 8

• n
• 2n
• 2n3
• 8n12
• 8n
• n