Adding and subtracting 2-step word problems

0:00- [Instructor] A school secretary started the school year with 450 markers. At open house, I should say at the open house. At the open house parents donated 163 markers. By winter break, 278 markers had been dried out or lost. How many usable markers does the school have now?

0:18Pause this video and try to think through that before we do this together. Alright, let's first try to visualize this with a strip diagram. So we start the school year with 450 markers. So let's say that this is, and I'm just eyeballing it so it's not going to be exact, but just to help visualize.

0:34So let's say that this is 450 right over here. So that's the number of markers that we start with. And at the open house, parents donated 163, so that's going to increase the number of markers we have. So lemme do this in another color. So they donated 163 markers, so we should increase by 163.

0:51So it looks something like this. We should increase by another 163. And then by winter break, 278 markers had been dried out or lost. So this is now taking away from our total number of markers. 278 had been dried out or lost. So we could take those away. The 278, maybe it looks something like this.

1:16278. And so this piece right over here is what is going to be left over. So we need to figure out this thing that I'm shading in, I guess you could say black. So first we could add 450 to 163 to get this total. And then we could subtract 278. So we're going to do 450 plus 163, plus 163.

1:40And then we're going to subtract 278. So first 450 plus 163, I can expand those out. That's the same thing. I'll do it. Let's see, I think I have space here. 400, at four hundreds plus five tens, that's 50, plus zero ones. And then I'm adding 163, that's 100, six tens and three ones.

2:08And if I add those two together, maybe in purple, I'm going to get three ones. I am getting 50 plus 60, that's 110 or 11 10s. Five plus six is 11, but we're in the tens place. So this is 11 10s or 110, and then 400 plus 100 is 500. So 500 plus 110. This part over here is 610 plus three, which is equal to 613.

2:38So this entire thing right over here, this whole thing is 613. And now we wanna subtract 278 from that. Well, we could use a similar technique. We could expand out, 613 is six hundreds plus one 10, plus three ones. And we're gonna subtract out two hundreds, seven tens, and eight ones.

2:59So minus 200, subtracting seven tens, and subtracting eight ones. Now when we do this, we can't subtract three from, eight from three. So let's take 10 from the tens place. So this becomes zero. We put the 10 here, this becomes 13. 13 minus eight is five. Now we have a problem in the tens place.

3:20We have no tens and we wanna subtract 70. So let's take a hundred from the hundred's place. So if we take a hundred, this becomes 500 and we put that a hundred over here, this becomes a hundred, and I get a hundred minus 70 is 30, and then I have 500 minus 200 is 300.

3:38So if 300 plus 30 plus five, which is three hundred and thirty five, three hundreds, three tens, and five ones. So that's how many usable markers the school now has, 335.