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
Find the value of nnn.
