That GCSE Maths question

I saw reports of a "twitter storm" last night about a maths GCSE exam being particularly difficult. The only question I saw in the tweets was n^2-n-90=0. This took me about 10 seconds to solve in my head. However, it later transpired that the full question was as follows (the colours may have been swapped, but the question remains the same):

Hannah has a bag with n sweets in it.
6 of the sweets are orange, the rest are yellow.
She takes one sweet from the bag, it is orange.
She takes another sweet from the bag, it is also orange.
The chances of taking 2 orange sweets from the bag is 1/3.
Prove that n^2-n-90=0

Now, I have to admit at 10pm I couldn't answer the question. I knew how to answer the question, but the time and the fact that I was 1/2 watching a re-run of QI meant I wasn't giving it my full attention.

This morning the same twitter storm was reported on the BBC website, so I thought I would give the problem a proper try. It took me less than 2 minutes. Now admittedly I have 2 math's O levels (that might give you the clue that I sat them in 1983 and 1984 respectively), maths A level and a degree in computer science, that involved some maths. However I haven't had to solve a quadratic equation for at least 25 years (to the point that I just had to use Google to remember the words "quadratic equation".)