In 2/4 minutes the number of revolutions a CD makes = 58 ½ = 117/2
Then
In 1 minute the number of revolutions the CD will make = [(117/2)/(2/4) ] * 1 = (117 * 4)/(2 * 2) = 117
So it can seen that the CD revolves at the rate of 117 revolutions per minute. I hope this is the answer you were looking for. The procedure for solving this problem is easy for you to understand i hope.