Percentages

• What is the easiest way to find a percentage of a number?

  Use the percentage button on a calculator
• How do you find 20 percent of 150 using a calculator?

  Place 20% x 150 on your calculator
• How do you convert a percentage into a decimal?

  Divide it by 100
• What is 20 divided by 100?

  0.2
• How do you find 20 percent of 150 using the decimal method?

  Multiply 0.2 by 150
• What is the fraction representation of 20 percent?

  20/100
• How do you find 20% of 150 using the fraction method?

  Multiply 20 over 100 by 150
• What is the simplified form of 20 over 100?

  1 over 5
• How do you find 1 over 5 of 150?

  Multiply 1 over 5 by 150
• Why can you convert a percentage into a decimal or fraction before multiplying?

  They all represent the same value
• How do you find 36 percent of 250 using a calculator?

  Multiply 36 by 250
• What is 36 divided by 100?

  0.36
• How do you find 36 percent of 250 using the decimal method?

  Multiply 0.36 by 250
• How do you find 36 percent of 250 using the fraction method?

  Multiply 36 over 100 by 250
• What happens when finding a percentage greater than 100?

  The answer will be larger than the number
• How do you find 145 percent of 60 using a calculator?

  Multiply 145 by 60
• What is 145 divided by 100?

  1.45
• How do you find 145 percent of 60 using the decimal method?

  Multiply 1.45 by 60
• How do you find 145 percent of 60 using the fraction method?

  Multiply 145 over 100 by 60
• How can exam questions be made more complicated?

  By using long sentences instead of direct questions
• How do you find the number of girls in a class of 25 pupils where 60% are girls?

  Find 60% of 25
• What is 60 percent of 25?

  15
• How do you find 40 percent of 25?

  Multiply 40 over 100 by 25
• What are the three techniques to find percentages?

  • Percentage button on a calculator
  • Decimal method (divide by 100)
  • Fraction method (put over 100)
• How to calculate percentage increases and decreases.

  
• Example of percentage decrease:

  
• An example of the Multiplier Method

  
• $Percentage\ Decrease\ =$$\ \frac{Original\ Value\ -\ New\ Value}{Original\ Value}\ x\ 100$
• To increase a value by a percentage:

  • Multiply by 1 + $\frac{percentage}{100}$
• To decrease a value by a percentage:

  • Multiply by 1 - $\frac{percentage}{100}$
• A positive answer = increase
• A negative answer = decrease
• REVERSE PERCENTAGES

  Finding the original amount before a percentage change.
• REVERSE PERCENTAGES

  $Original\ price\ =$$\ \frac{sale\ price}{percentage\ paid\left(as\ decimal\right)}$
• VAT

  VAT is a tax added to the price (usually 20%).
• VAT (Example)

  TV costs £300. Add 20% VAT.20% of 300 = 60 → Final price = £360