There are 2 white buttons and x x\,x black buttons in a box.
2 buttons are taken from the box at random.
The probability that both buttons are black is 1522\displaystyle \frac{15}{22}2215.
Work out the value of xxx.
Practise OCR GCSE Maths Probability Equation Questions with exam-style questions for Foundation and Higher tier. 28 questions, matched to the OCR GCSE Maths (J560) specification and written in the written papers 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.