You could convert the hours into minutes first, but it's easier to convert the minutes to hours, because 30 mins is half an hour. Each hour is "worth" two half-hours, so 30 hours is 60 half-hours, and therefore half an hour is 1/60 of 30 hours. Percentage is the same fraction of 100 and 1/60 of 100 is 1/60*100=100/60=5/3=1.67% approx.