1. Probability 100% 50% 0% 1 0.5 ½ Will happen Won’t happen
e.g throw a normal dice and score between 1 and 6
Won’t happen
e.g throw a normal dice and score 7
0.5
Equally likely to happen or not
e.g throw a normal dice and score an even number

2. If all the possible outcomes are equally likely
P(something happening) = e.g. On a normal dice P(throw a number less than 3) = Always simplify a probability fraction if you can.

3. If you are finding the probability of two things which do not depend on each other you can use a 2 way diagram. e.g Find the probability of getting heads on a coin and an odd number on a dice.
Possible outcomes for dice 1 2 3 4 5 6 H
H 1
H 2
H 3
H 4
H 5
H 6 T
T 1
T 2
T 3
T 4
T 5
T 6 1 2 3 4 5 6 H T
Possible outcomes for coin

4. You can calculate almost any probability with a tree diagram Find the probability of getting two heads and one tail in 3 flips.

5. Comparing probabilities
With a calculator you can:
Compare probabilities as a decimal 3÷5 = 0.6 etc
Compare probabilities as a percentage 3÷5 x 100 = 60%
Without a calculator you must make them into equivalent fractions

6. Using probabilities to make predictions
Once you have a probability you can make a prediction
e.g
1) the probability of getting a head with a coin toss is ½
Toss a coin 30 times
expect heads ½ x 30 times = 15 times
2) probability of throwing a 7 on two dice is
Throw two dice 30 times
expect heads 1÷6 x 30 times = 5 times