3. Ratio
• A method to compare the relative
quantities of 2 or more items.
• eg. Squash is made using the ratio
• For every 1 part of juice, we need 5
parts of water
• We say Juice to Water in the ratio 1 to
5
Juice : Water
1 : 5
4. Equivalent Ratio
• If we mix orange squash using Sugar
and Water in the ratio 1 to 20.
• Using 5 measures of Sugar, how many
measures of water do we need ?
Sugar : Water
1 : 20
5 : 100
20 x 5
multiply
by 5
5. Cancelling ratios
• Like fractions, cancel to simplest form
• When you are given the quantity of
each item and asked to convert to a
ratio
• eg. With 4 green balls and 12 yellow,
what is the ratio of red to blue balls ?
green : yellow
4 : 12
1 : 3
Divide
both sides
by 4
6. Splitting ratios
• Share £36 in the ratio 2:7
• 1- How many parts in ratio ?
• 2- What is 1 part worth ?
• 3- Multiply up ratio
• 4- Add together to check
2 + 7 = 9
4£369
2 : 7
£8 £28
£8 + £28 = £36
X4 x4
8. Probobality
The meaning of probablity:
Probablitly is the chance of a particular
outcome happening.
Probablity os a number between 0 and
1
Probablity= no.of actual outcome
no. of possible outcomes
9. Independet events
These are events/outcomes that are independent of eachother.
This means that one has no effect on the other (eg rolling two
dice).
• The AND rule is used to relate the probability of two
independent events occuring.
• If P(M) is the probability of an event M happening and P(N) for
an event N. Then the probability of both events occuring is
given by:
• P(M + N) = P(M) x P(N)
10. Mutally exclusive
• Events are said to be mutually exclusive if
they cannot happen at the same time.
• The OR rule is used to relate the
probability of one independent event
happening or another independent
event happening at the same time.
• The probability of event M or another
event N, when the two are mutually
exclusive, occuring is given by:
• P(M or N) = P(M) + P(N)
