Solving equations and inequalities through substitution example 2

Mario started the day with five fire flowers. He used some, and now only has three left. If u is the number of flowers he's used, we can write the following equation: how many fire flowers did Mario use?

So, he started with five, he uses some of them, so we subtract the number he used and he ends up with three. There are a bunch of ways that you could do it. One way is you literally could probably do this in your head.

"Hey, I took away some number from five, and I got three!" You probably know, "Hey, well, if I take two away from five, I'm going to get three." So, he used two flowers.

The other way that you could think about doing it is, "Well hey, we got only four options here. Let me substitute each of them in here." Maybe I was able to do this one in my head, but if I had something more complicated, let me try out these choices.

So if he only took a zero away, it'd be five minus zero; he'd still, of course, be left with five. If he took one away, then of course he'd only have four left. If he took three away, he'd have two left. But if you took two away, five minus two is indeed three.

The third way you'll learn this as we go into more of how algebra works, and also the why, is that you could systematically solve it, but we'll go into that in future videos.

So, he used two fire flowers.