A college has 1,250 sanctioned seats. After the first round of admissions 12% of them were still vacant, and in the second round 40% of those vacant seats were filled. What per cent of the sanctioned seats are still vacant?

Vacant after round one = 12% of 1,250 = 150. Round two fills 40% of those, that is 60, leaving 90 vacant: 90/1250 = 0.072 = 7.2%. Shortcut: 60% of 12% = 7.2%. 4.8% is 40% of 12%, the seats FILLED in round two rather than those still empty. 40% simply repeats the round-two rate, and 52% adds 12 and 40 as though both were shares of the sanctioned strength - the 40% is a share of the 150 vacancies only.