You are correct, this is a discrete distribution so the cdf's are therefore a summation and not an integral. This is sloppy notation in the examiners report. As for whether you are marked down for giving the right answer using the right method, that is entirely up to the examiner!
A nice question to start the paper though, guaranteed 10 marks if you get one of these (providing the examiner is skilled enough to mark your answer correctly)
Last edited by a moderator: Aug 4, 2018