Representing multi-step problems: equations
About this video
A library gets 145, 152 and 200 donated books, and all of them are shared equally onto 7 shelves. The video shows how to plan the steps (add all the books, then divide by 7) and uses that plan to pick the correct set of equations and rule out the wrong ones.
You'll be able to
- decide which operations a multi-step word problem needs.
- choose a set of equations that matches the steps of a word problem.
- explain why an equation with the wrong operation does not fit the story.
Key words
- equation
- A number sentence with an equals sign that shows two amounts are the same, like 297 + 200 = 497.
- divided equally
- Split into groups that each have the same amount.
- total
- The amount you get when you add everything together.
Transcript
- [Instructor] We're told a library has a book donation event. Community members donate 145 books. A publishing company donates 152 books. A local bookstore donates 200 books. All of the books are divided equally onto seven shelves. Which set of equations can be used to find b, the number of books on each shelf?
So pause this video, have a go at it, before we work through it together, before we work through it together. Okay, now let's do it together. And I'm not even going to look at the choices. I'm just gonna think about how I would actually try to approach this. So the first thing I wanna do is I want to add up all of these, because what's happening is we're looking at the total number of books, and then we wanna divide that equally into seven shelves.
So I would think about it. I would take 145, and, to that, I would add the 152 books from the publishing company, and, to that, I would add the 200 books from the local bookstore, and then I would divide that total, 'cause all of the books are divided equally into seven shelves.
They tell us that right over there. So then I would just divide everything by seven. Now when I look at these choices, I don't exactly see that. So it looks like they broke down the steps a bit. So choice A, they start off adding 145 and 152 to get 297, which looks right, so it looks like they added this first.
And so the next thing I would do is add 200 to that. And it does indeed look like they did that next to get to 497. So then they added all of this together to get to 497, and then they multiplied by seven. No, we wanna divide by seven, so I'm going to rule this one out.
All right, the second choice, they did the same first step. They added these first two numbers to get to 297, then they added 200 to that to get to 497, so I'm liking this so far, and then they divided by seven right over here, which is exactly what we thought of doing originally.
So I like choice B. But let's just see what's wrong with choice C. Choice C, they did the same first step, 145 plus 152 is equal to 297, but then, for some reason, they subtracted 200. Now that would've made sense if the library was donating 200 books, giving it to someone else, but this is a bookstore donating it to the library, so we don't wanna subtract it out.
So that's where choice C does not work.
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