单选题
A circular rim 28 inches in diameter rotates the same number of inches per second as a circular rim 35 inches in diameter．If the smaller rim makes X revolutions per second，how many revolutions per minute does the larger rim make in terms of X?
【正确答案】
C
【答案解析】Since the smaller rim has diameter 28 inches and rotates x revolutions per second, it rotates 2Snx inches per second. If y represents the number of revolutions the larger rim rotates per second, then the larger rim rotates 35πy inches per second. Since the rims rotate the same number of inches per second, it follows that 28πx = 35πy.Then y =28x/35=4x/5 inches per second or 4x/5(60) = 48x inches per minute.The correct answer is C.