Section 4: Ratios Flashcards
How to write a ratio as a fraction
Put one number over the other
If the ratio contains decimals
Multiply till it doesn’t then simplify
What to fo when the ratio changes
(E.g 3 of the chickens fly away so now there’s only 2 chicken for every 8 horse instead of 5)
Find origional number
Work out remaining number by subtracting the origional by the amount that have gone
In direct proportion
If one number increases the other increase by same amount
In inverse proportion
When one side increase the other decreases by same amount
What is the equation for y is proportional to x
Y = kx
What is the equation for y is inversly proportional to x
Y = k÷x
How to find x percent of y
Divide x by 100 then times by y
How to find a new amount after a x percent change
Divide x by 100 then add 1
Multiply origional value by this
How to express x as a percentage of y
Divide x by y then multiply by 100
How to find percentage change
( questions will say find percentage increase/ profit/ error or percentage decrease/ loss/ discount
Percentage change = change ÷ origional x 100
Finding origional value
Write the amount in the question as a percentage of origional value. Eg an increase of 10.5 percent = 110.5 percent of origional value
Divide to find 1 percent of origional
Multiply by 100 to give origional value
What does simple interest mean
A certain percentage of the origional amount only is paid at regular intervals. The amount of interest is the same every time its paid
How to work out simple interest questions
Work out interest in 1 year
multiply by amount of years
What does compound interest mean
The amount added or taken off changes each time. Its a percentage of a new amount rather than the origional
