Good question. Managed to get it wrong by not noticing that decimal wasn't decimal(7,2). Probably wouldn't have got it right even if I'd noticed.
There seems to be something wrong with the percentage calculations in the result counts. with 4 answers so far we have 50% (2) wrong and 50% (2) right but for the individual selections 0,1,2,3,4 we have 0%,50%,0%,0%,25% which is crazy.