Conditional probability

Angela chooses one number randomly from 1, 2 and 3. She then chooses another number randomly from 4, 5 and 6. She adds these two numbers to get the total.

May/June 2025

The chance that the school bus arrives late is $\frac{9}{10}$. When the school bus is late, the chance that Seb goes on the bus is $\frac{15}{16}$. When the school bus is on time, the chance that Seb goes on the bus is $\frac{3}{4}$.

Oct/Nov 2019

Sachin chooses one number at random from the first three multiples of 3, then chooses one number at random from the first three prime numbers. He adds these two numbers to obtain a score. A table is displayed with multiples of 3 as $3$, $6$, $9$ and prime numbers as $2$, $3$, $5$, with some of the scores already filled in.

Oct/Nov 2021

Katy chooses one number at random from 2, 3 and 5, and then selects one number at random from 5, 6, 7 and 9. The sum of the two chosen numbers is even.

Oct/Nov 2022

The diagram displays two fair dice. Dice A is labelled 1, 2, 2, 2, 3, 6. Dice B is labelled 2, 3, 3, 4, 4, 4.

Oct/Nov 2023

75 people are surveyed about whether they own a car, $C$, and whether they have a job, $J$. The Venn diagram displays the outcomes. There are 9 in $C$ only. There are 51 in the overlap of $C$ and $J$. There are 13 in $J$ only. There are 2 outside both circles.

Oct/Nov 2024