10. Probability

Question 1

Probability of an event

Answer 1

Probability of an event = no. of ways an event can occur / total no. of outcomes

Question 2

Probability properties

Answer 2

• If an event cannot happen, probability = 0
• If an event is certain to happen, probability = 1
• Probability always lies between 0 and 1
• Probabilities are written as fractions or decimals

Question 3

p(event A) + p(not event A) = ?

Answer 3

p(event A) + p(not event A) = 1

Question 4

Exclusive events

Answer 4

Two events are mutually exclusive if they cannot occur at the same time

Therefore you have to ask the probability of one event occurring OR another event occurring.

Question 5

Finding the probability of 2 exclusive events occurring

Answer 5

p(A or B) = p(A) + p(B)

Question 6

Independent events

Answer 6

Two events are independent if the occurrence of one event is unaffected by the occurrence of the other.

Therefore they can both happen (they aren’t exclusive)

Question 7

The probability that two independent events occur…

Answer 7

p(A and B) = p(A) * p(B)

Question 8

Conditional probability

Answer 8

Conditional probability is the probability of an event, given that another event has occurred.