Think about it: You know that 30 minutes is half of an hour. You know that .5 of an hour is 30 minutes. Can you break 30 minutes into half? Yes, it's 15. Can you divide 45 by 15? Yes, it's 3. So, now you know that 45 minutes is 3/4 of an hour, or .75 (just like 3 quarters of a dollar is 75 cents)