Double subtraction 2-step word problem
About this video
A theater has 614 seats: 137 red, 228 yellow, and the rest green. The narrator uses a strip diagram to see that he must subtract both colors from the total. He finds 614 - 137 = 477 and then 477 - 228 = 249 green seats, regrouping along the way.
You'll be able to
- use a strip diagram to find an unknown part.
- solve a two-step problem by subtracting twice.
- subtract three-digit numbers by regrouping tens and hundreds.
Key words
- strip diagram
- A drawing with bars that shows the parts and the whole of a problem.
- total
- The whole amount, here all 614 seats.
- regroup
- To trade a ten for 10 ones, or a hundred for 10 tens, so you can subtract.
- place value
- The value of a digit depending on whether it is in the ones, tens or hundreds place.
Transcript
- [Instructor] We're told a movie theater has 614 seats, 137 seats are red, 228 seats are yellow, the rest of the seats are green. How many seats in the theater are green? Pause this video and see if you can figure that out. Well, let's first visualize this a little bit.
So we have 137 seats that are red. I'll use a little strip here to show 137. Then we have 228 seats that are yellow. So I'm approximating, let's call that 228. 228 that are yellow. And then we have some number that are green. The rest of them are green. So I will put a question mark here.
And we know that the total number of seats is 614. They tell us that right over there. Lemme do that in that another color right over here. The total number of seats is 614. So what is going to be the number of green seats? Well, you could take the total, 614, and if you subtract 137 and you subtract 228, then you'll be left with this little green part.
So we need to subtract 137 and subtract 228 to get to the green, number of green seats. So let's do this. And we could do the 614 minus 137 first. And to do that, I am going to actually break out the 614. You can think about it breaking into their place values.
We have six hundreds, which I could view as 600 plus one 10, which is the same thing as 10, plus four. That's 614. And I wanna subtract 137. Well, that's the same thing as subtracting 100, subtracting 30, and subtracting seven. And so what would this be equal to?
Well, I could go to the ones place. Well, I can't subtract seven from four, so let me see if I can regroup a little bit. Let's see if I took 10 from the tens place. So if this becomes zero right over here. So I have nothing there. But then I take that 10, put it here, I get 14, and now I can figure out 14 minus seven is equal to seven.
Now I have a problem in the tens place right over here, zero minus 30. I can't do that. So let me take 100 from the hundreds place. So let me take 100 out of here. So this is gonna be 500. And let me put that 100 over here. So I have 100. Now I can do a hundred minus 30 is equal to 70.
And then I have 500 minus 100, which is equal to 400. So 400 plus 70 plus seven, which is 477. That's just this part right over here is 477. And now I have to subtract 228 and I could do the same thing. I could expand out 477, that's 400 plus 70 plus seven, four hundreds, seven tens, seven ones.
And I'm gonna subtract two hundreds. minus 200, two tens, minus 20, that's two tens here, minus eight. I'm subtracting out this whole, all the parts of it. And so what is that going to be equal to? Well, same idea. I can't subtract eight from seven. So let me take 10 from the tens place.
So if I take 10 from here, this becomes 60 and I put that 10 here, this becomes 17. And so if I have 17 minus eight is nine, 60 minus 20 is 40, and 400 minus 200 is 200. So I have 200 plus 40 plus nine, that is 249. And I should have made this bigger if I wanted to actually make it to scale.
But that's how many of the seats are actually green.
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