There are n n\,n counters in a bag.
8 of the counters are red and the rest are blue.
Adam takes a counter from the bag at random and does not replace it. He then takes another counter at random from the bag.
The probability that Adam takes two blue counters is 15\displaystyle \frac{1}{5}51
Write the equation in the form n2−21n+90=0n^2 - 21n + 90 = 0n2−21n+90=0.
Verify that the value of n n\,n is 15.
43 exam-style questions on OCR GCSE Maths Probability Equation Questions. Each one has a worked solution and a mark scheme showing where the marks go.