The probability that an event will occur is the proportion of times the event is expected to happen in a suitably large experiment.

Probabilities involving algebra

Maths

In this unit, pupils use their knowledge of calculating theoretical probabilities and extend this understanding to calculating conditional probabilities using all of the representations encountered in the prior unit.

Conditional probability

Lucas spins a spinner with colours: {green, orange, brown}. 
P(green) = 30%.
P(orange) = P(brown).
P(brown) = {{ }}%.

Izzy plays a game she can either win (W), lose (L), or draw (D)
P(W) = 0.55.
P(L) is twice as likely as P(D). P(D) = {{}}.

A game can either be won by Alex, Sam, or Jacob.
By constructing and solving an algebraic equation, find P(Sam wins).

A spinner with outcomes {A, B, C, D} is spun once.
P(A) = 0.12.
P(B) = $$x$$.
P(C) is twice as likely as P(B).
P(D) is equally likely as P(A or C).
Find an expression for P(D) in terms of $$x$$.

A bag of marbles only contains white (W), green (G), and cyan (C) marbles.
36% of the marbles are white.
P(G) : P(C) = 3 : 5.
P(C) = {{}}%.

A bag of sweets only contains four flavours. The table shows the frequency of each type of sweet in the bag. 
P(cherry) = $$3\over10$$.
The number of apple sweets in the bag is {{ }}.

Here are two decks of cards.
A single card from Deck 1 and a single card from Deck 2 is drawn to make a pair.
There are {{ }} possible outcomes for drawing one card from each deck.

Here are two decks of cards. A single card from Deck 1 and a single card from Deck 2 is drawn to make a pair.
What is the probability that this pair of cards contains an odd number?

The outcome 7 isn’t in either event A or event B. 

Events A and B are not mutually exclusive. 

Each face on an 8-sided die has a unique integer from 1 to 8 written on it.
The Venn diagram shows Event A = {factors of 15} and Event B = {even numbers}.
Which of these statements are correct?

Sam plays a video game that can either be won or lost.
The probability that Sam wins the video game is 61%.
The probability that Sam loses the video game is {{}}%

This table shows the mutually exclusive and exhaustive set of outcomes, and the probability of each outcome, from spinning a spinner once.
Find the value of $$x$$.

This table shows the set of outcomes and the probability of each outcome, from spinning a spinner once.
The spinner is spun 1000 times. How many times should you expect the spinner to land on C?

Starter Quiz