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## Two-step equations intro

Current time:0:00Total duration:2:34

# Setting up 2-step word problems

CCSS Math: 3.OA.D.8

## Video transcript

- [Instructor] My book is 58 pages. I have already read 13 pages. I plan to read five pages each day until I finish the book. Which equation could I use to find out how many days, d, it will take
to finish reading the book? So pause this video and see
if you can figure that out. Okay, so let's first think about the important
information they're giving us. They're giving us the number
of pages that are in the book. They're giving us how
much we've already read. We've already read 13 pages. And they also tell us
how much we plan to read. I plan to read five pages each day until the book is finished. And then we want an
equation that could use to find how many days. And d is how we're going to
represent the number of days, let me do it in the same color, it'll take to finish reading the book. All right, so if we knew how
many pages we have to read and we were divided by the fact that we're reading five pages per days, well, then that would give
us the number of days. So how many pages do we have
left to read in the book? Well, the book is 58 pages. We've already read 13, so we
could subtract out 13 of those. So this expression right over here, this is how many pages
we have left in the book. Let me write that down. How many pages left. And if we wanna figure out
how many days it's going to take to read these, we would divide this by how
many pages we read each day. And we see that we read
five pages each day. So if we divide this by five,
then this whole expression, let me do it in this color, this whole expression is going to tell us how many days left. How many days left. And so this is going to be equal to d 'cause d is the number of days left to finish reading the book. Now, if we look at these choices, that's exactly what we have
right over here in choice C. We can make sure that these
others don't make sense. 58 plus 13, no, that would be a situation where we're reading 13 pages more than the number of pages
that are in the book. That doesn't make sense. And that's happening for
both choice A and choice B. It would also not make
sense to multiply by five because it's not going to
take you five times more than the number of pages to read the book. You're going to divide by five. You're reading five pages every day. And we are done.