There are n n\,n counters in a bag.
4 of the counters are red and the rest are blue.
Ross 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 Ross takes two blue counters is 13\displaystyle \frac{1}{3}31
Show that n2−13n+30=0n^2 - 13n + 30 = 0n2−13n+30=0
Find the value of nnn.