Maths Revision

Lesson 1

• Created by: Niamh
• Created on: 13-05-10 17:42

Question

Percentage Change Using A Multiplying Factor

A multiplying factor is a decimal which is equivalent to the percentage that you want to add up with.

Find 89% of £46.20

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89% divided by 100 = 0.89

0.89 x 46.20= £41.118

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Question

Simple Interest

This is when the interest is calculated at the beginning of the investment and the amount added each year is the same.

£450 is deposited in a simple interest account which earns interest at a rate of 4.5%. How much will be in the account after 10 years?

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Original Ammount + Years x Original Ammount x Multiplying Factor For Interest Rate

450 + 10 x 450 x 0.045 = £9315

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Questions

Compound Interest

This is when the interest earned is recalculated at the end of each year so the ammount added changes.

£450 is deposited in a compound interest account which earns interest a rate of 4.5%. How much will be in the account after 10 years?

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100 + 4.5 = 104.5% = 1.045

450 x 1.045 to the power of 10 = £4702.5

Original Ammount x (Multiplying Factor For The Increase 100 + Interest rate)Years

To find the multiplying factor for a decrease do 100 - percentage then change to a decimal.

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Question

Finding A Total From A Percentage

This involves using the fact that percentages are out of 100 to find the original 100%'s value.

15% of an ammount is £3.60. How much is the whole ammount?

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5% = 3.60 divided by 3 = 1.20

100% = 3.60 divided by 3 x 20 = £24

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Question

Reversing Percentage

In a sale a table cost £860. The sale says 20% off, how much would it have cost before the sale?

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20% = 0.8

Original Ammount x 0.8 = Sale Price

Original Ammount = 860 divided by 0.8 = £1075

80% = 860

100% = 860 divided by 0.8 = £1075

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Question

Writing As A Ratio

Ensure the units are the same and then simplify as you would a fraction. Remember that the final answer should not contain decimals or units.

Write 0.64kg to 320g as a ratio

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640g : 320g

640 : 320

2 : 1

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Question

Using Ratios

Using the fact that a ratio tells you how many parts belong to each item / person, link it to fractions to decide what to do.

Share £35 in the ratio 2 : 5

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2 + 5 = 7 parts

35 divided by 7 = £5 per 1 part

2 x 5 = £10

5 x 5 = £25

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