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
89% divided by 100 = 0.89
0.89 x 46.20= £41.118
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?
Original Ammount + Years x Original Ammount x Multiplying Factor For Interest Rate
450 + 10 x 450 x 0.045 = £9315
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?
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.
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?
5% = 3.60 divided by 3 = 1.20
100% = 3.60 divided by 3 x 20 = £24
In a sale a table cost £860. The sale says 20% off, how much would it have cost before the sale?
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
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
640g : 320g
640 : 320
2 : 1
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
2 + 5 = 7 parts
35 divided by 7 = £5 per 1 part
2 x 5 = £10
5 x 5 = £25