Percentages of shapes

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# Percentages of shapes - PowerPoint PPT Presentation

Percentages of shapes. Estimating percentages. Estimating percentages. Equivalent fractions, decimals and percentages. Table of equivalences. Table of equivalences. Ordering on a number line. Dominoes. Calculating percentages mentally. Some percentages are easy to work out mentally:. 1\%.

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## PowerPoint Slideshow about 'Percentages of shapes' - seanna

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Presentation Transcript
Calculating percentages mentally

Some percentages are easy to work out mentally:

1%

Divide by 100

To find

10%

Divide by 10

To find

25%

Divide by 4

To find

50%

Divide by 2

To find

Calculating percentages mentally

20%

30%

60%

15%

75%

11%

2%

49%

150%

17.5%

0.5 %

We can use percentages that we know to find other percentages.

Suggest ways to work out:

Finding the original amount

We can use a unitary method to solve these type of percentage problems. For example,

Christopher’s monthly salary after a 5% pay rise is £1312.50. What was his original salary?

The new salary represents 105% of the original salary.

105% of the original salary = £1312.50

1% of the original salary = £1312.50 ÷ 105

100% of the original salary = £1312.50 ÷ 105 × 100

= £1250

This method has more steps involved but may be easier to remember.

Finding the original amount

actual increase

Percentage increase =

× 100%

original amount

actual decrease

Percentage decrease =

× 100%

original amount

Sometimes, we are given an original value and a new value and we are asked to find the percentage increase or decrease.

We can do this using the following formulae: