GCSE · Basic probability

Probability of a single eventExam-style questions

Why a probability is a share of the whole — so it lives between 0 and 1, why P(A) = favourable ÷ total needs equally likely outcomes, and how the "it all adds to 1" rule drives complements, missing table entries and expected numbers.

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13 questions · GCSE (Higher) level · mark scheme and worked solution on each · no sign-up to try

DifficultyAll Level 1 Level 2 Level 3 Level 4 Level 5

1
A biased four-sided spinner can land on 1, 2, 3 or 4.

The table shows information about the probability that the spinner lands on each number. The spinner is equally likely to land on 3 as it is to land on 4.
Number 1 2 3 4
Probability 0.15 0.35 $y$ $y$
(a) Work out the value of $y$ .

The spinner is spun 200 times.

(b) Work out an estimate for the number of times the spinner lands on an even number.
Level 4 · 6 marksTry it
2
Priya plays one game of chess each week. Each game she either wins, draws or loses.

The probability that Priya wins a game is $\frac{2}{5}$ .

The probability that Priya draws a game is $15\%$ .

(a) Work out the probability that Priya loses a game. Give your answer as a decimal.

(b) Priya plays 60 games. Work out an estimate for the number of these games that Priya loses.
Level 4 · 5 marksTry it
3
A bag contains only red counters and yellow counters.

There are 12 red counters in the bag.

A counter is taken at random from the bag. The probability that it is red is $0.3$ .

(a) Work out the total number of counters in the bag.

(b) Work out the number of yellow counters in the bag.

A counter is taken at random, its colour is recorded, and the counter is put back in the bag. This is done 250 times.

(c) Work out an estimate for the number of times a yellow counter is taken.
Level 4 · 5 marksTry it