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
Show that n2−21n+90=0n^2 - 21n + 90 = 0n2−21n+90=0 and hence find the value of nnn.
43 exam-style questions on Eduqas GCSE Maths Probability Equation Questions. Each one has a worked solution and a mark scheme showing where the marks go.