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Substituting variables and simple equation

Video transcript
Mario started the day with 5 fire flowers. He used some and now only has 3 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 5. He uses some of them, so we subtract the number he used, and he ends up with 3. So there's 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 5, and I got 3. And you probably know, hey, well, if I take 2 away from 5, I'm going to get 3, so he used 2 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 you only took zero away, it would be 5 minus 0. He'd still, of course, be left with 5. If you took 1 away, then of course, he'd only have 4 left. If he took 3 away, he'd have 2 left. But if he took 2 away, 5 minus 2 is indeed 3. And the third way, you'll learn this as we go into more of the how of algebra, and also the why, is that you could systematically solve it. But we'll go into that in future videos. So he used 2 fire flowers.