In a jar there are only white marbles, black marbles, orange marbles and purple marbles.
A marble is taken at random from the jar.
The table shows the probabilities that the marble will be orange or will be purple.
| Colour | White | Black | Orange | Purple |
|---|---|---|---|---|
| Probability | 0.25 | 0.15 |
The probability that the marble will be black is three times the probability that the marble will be white.
There are 20 orange marbles in the jar.
Work out the number of black marbles in the jar.
Practise AQA GCSE Maths Probability with exam-style questions for Foundation and Higher tier. 212 questions, matched to the AQA GCSE Maths (8300) specification and written in Paper 1, Paper 2 and Paper 3 style. Every question includes a full worked solution and mark scheme, so you can see where marks are awarded rather than just whether you got the answer right.
