How to Solve Word Problems

Video Transcript

"Let's look at how to solve a word problem. The key with a word problem is to identify the formula that you need. That's step one. Step two: plug into that formula. Plug in what you know. And step three: solve for what you don't know. So the word problem, really, once you plug into a formula, it stops being a word problem. And at that point, it's just algebra, just simple algebra. Let's see. So we have a question here: "Xena drove 10 miles to school. If it took her 25 minutes, how fast was she driving?" So this is a distance equals rate times time, D=RT, probably the single favorite formula of math textbooks. So we plug in what we know. Just look through the question and hunt for what you know. So do we know D? Xena drove 10 miles. Bingo. So she drove 10 miles. That's the distance. If she drove 10 miles, that's not her speed or her time. Right? So it took her 25 minutes. That's the time. So it took her 25 minutes. So what we don't know is R. So that's what we're going to solve for. So step one: identify the type of formula. Step two: plug in what you do know. Step three: solve for what you don't know. So in this case, there's one variable we don't know, and it's rate. And in fact, how fast was she going, that's what they want. No coincidence. So to get R then, we divide both sides by 25. Cancels, that's why we did it. R alone equals 10 over 25. As always, if ever you can simplify or reduce a fraction, you should. So 10 over 25, 5 goes into both the top and bottom. 10 divided by 5 is 2. 25 divided by 5 is 5. So we get two miles per five minutes. That doesn't make a lot of sense to people. You don't really think of things in miles per minute. So let's change it to miles per hour. The way we would do that is since this is miles, we're happy with that. We don't want to change that. But this is minutes. We don't want that. So we're going to do is we're going to multiply by 60 minutes is 1 hour. That's the conversion. And you can see that minutes is going to cancel, which is what we want, leaving us 2 times 60 is 120 on the top. And that's miles over 5 times 1 is 5 hours. So we have 120 miles per hour. As always, if you can reduce a fraction, you should. 120 divided by 5 is 24 miles per hour. So Xena drove 24 miles per hour to school."