In a box there are only red pens, blue pens, black pens and green pens.
A pen is taken at random from the box.
The table shows the probabilities that the pen will be red or will be green.
| Colour | Red | Blue | Black | Green |
|---|---|---|---|---|
| Probability | 0.42 | 0.14 |
The probability that the pen will be black is three times the probability that the pen will be blue.
There are 28 green pens in the box.
Work out the number of black pens in the box.
Practise Oxford AQA IGCSE Maths Probability with exam-style questions for Core and Extended tier. 28 questions, matched to the Oxford AQA IGCSE Maths (9260) specification and written in Paper 1 and Paper 2 (Core: 1C and 2C; Extension: 1E and 2E) 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.