A district blood bank's record shows that four years ago it collected 12,000 units in all, 40 in every hundred of them at camps held away from its premises; last year it collected 9,000 units in all, 55 in every hundred of them at such camps. Which of the following must be true?

Four years ago the camps gave 4,800 units and everything else 7,200; last year the camps gave 4,950 and everything else 4,050. So collection away from camps fell, which is the first option. Camp collection actually rose slightly, so the second is false; the number of camps held is nowhere recorded and a larger yield could come from fewer camps, so the third cannot be settled; and 40 in every hundred is not more than half, so the fourth is false.