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.

Math Tip of Week -- Algebra: Why Are There Letters in Math??

Take a look at the word equation. It has the same root as the word equal. An equation is a situation in which one thing is the same as something else. In math, it means that one number or set of numbers is equal to another number or set of numbers. That's why there is an equal sign (=) in the middle of it.

For example, we know that 2 + 2 is the same thing as 4. We say 2 + 2 = 4. The numbers on both sides of the = mean the same thing.

But what if we only have two numbers in that equation? What if we only have 2 + 2 =
and we don't know what goes on the other side of the =? We substitute the missing information with a letter (usually x, y or z) to represent that we don't know the number yet.

We could write 2 + 2 = x.
To solve for x, we must first isolate x, or get it alone, on one side of the =. In this example, x is already by itself, so we only have to add 2 + 2 to find it.

Simplified, it looks like this: 2 + 2 = x
2 + 2 = 4
x = 4

Let's do another one, and mix it up a little: 2 + x = 4
We need to isolate the x. We know that 2 + something is equal to 4, so 4 - 2 must be equal to that something: 4 - 2 = x. And we have the x right where we want it. Now we just need to solve to find x.

It looks like this: 2 + x = 4
4 - 2 = x
2 = x

Now let's look at a problem like this: 3x = 6
This means that 3 times something is 6 . . . but what is that something?
We follow the same steps: isolate x and solve the problem like this: 3x = 6
x = 6/3
x = 2

Now let's make it a little harder: 3x + 4 = 12
3x = 12 - 4
3x = 9
x = 9/3
x = 3