Math Tip of the Week -- Subtracting Time

Subtracting time is no different than subtracting other numbers. We know that if all of the digits on the top are bigger than all of the numbers on the bottom, we just subtract straight down. The same goes for time.



But what happens if we have to borrow? When subtracting time, we don't so much borrow as we convert. If we borrow from the hours column, we must add the number of minutes (the equivalent to the hours we borrowed) to the minutes column. It looks like this:

We would use the same process for subtracting units of measure, too. But we would use the equivalent numbers for the measures we're working with. For example, 1 foot = 12 inches, 1 pound = 16 ounces, etc.