Sal solves length word problems with addition and subtraction.
- Dominique drew a 72 centimeter line on the playground with blue chalk. So the line that she drew, maybe it looks something like that. And that is 72 centimeters, 72 centimeters long. So from there to there is 72 centimeters. And another line with pink chalk that is, so let's do this with pink chalk, another line with pink chalk that is 14 centimeters longer than the blue line. So let me draw the other line. So the other line, whoops. The other line is going to be 14 centimeters longer. So maybe it looks something like that. So it's definitely going to be longer. And it's 14 centimeters longer, so if we go from here to here, that's going to be the same, should maybe make it the same length, this is going to be the 72 centimeters. That's 72 centimeters. But it's also another 14 centimeters. So it's gonna be 14 centimeters longer. So how long is a pink chalk line that Dominique drew? Well you would just add the 72 plus 14. So 72 plus 14 is equal to, two ones plus four ones is six ones, seven 10s plus one 10 is eight 10s. So this longer line here is going to be 86, 86 centimeters. Let's do another one. So we're told a cable on the Golden Gate Bridge is 33 meters long. Another cable is 13 meters longer than the first cable. Let me do this in a different color. Is 13 meters longer than the first cable. How long would the cables be if lined up end to end? So they're not just saying, "How long is the longer one?" Like they did in the last example. They want to know how long are the cables if you line them up end to end? So this first cable is 33 meters. Let me draw it this way. So the first cable is 33 meters long. 33, and actually why don't I draw it this way, because this is what the cables would actually look like. So this cable is 33... 33 meters long. Another cable is 13 meters longer than the first cable. So this other cable right over here is 13 meters longer. So this cable right here is 13 meters longer. So what's the length of this cable? Well it's going to be the length of the first one, 33, plus 13. It's 13 meters longer. Plus 13, that gets us... three plus three is six, three plus one is four. This one over here is gonna be 46 meters. Now they didn't just ask, "How long is the second cable," which is 46 meters. They're asking, "How long would the cables be "if we lined them up end to end?" So if we lined the 33 meter one, so if we lined up the 33 meter one, and then right next to that, we, right next to that, put the 46 meter one. So if we did something like that. Well we know that this one over here is 33 meters, and the next one is 46 meters, so we would have to add 33 plus 46 to figure out how long they would be end to end. And what is that gonna be? So if we say 33 plus 46, plus 46, three ones plus six ones is nine ones, three 10s plus four 10s is 70, sorry... three 10s plus four 10s is seven 10s. So it's going to be 79 meters if we line them up end to end. Let's do one more. Reynaldo has a 36 centimeter scarf. So he has a 36 centimeter scarf. He decides to cut out part of the scarf so it is now only 19 centimeters. How many centimeters did Reynaldo cut off of his scarf? So let's draw his scarf. So it was a 36 centimeter scarf, so it might've looked something like this. So this was his scarf before, if I stretch it all out, and it is 36 centimeters, 36 centimeters long. But he cuts part of his scarf so it's only 19 centimeters long. So now it is only 19 centimeters. So after he cut it, it's gonna look something like this. Actually maybe I'll... actually, I'll draw it in green again. So after he cuts it, his scarf is gonna look something like this. It's gonna look something like this, where now it's only 19 centimeters. 19 centimeters. So how much did he cut off? Well what he cut off is going to be the difference between 36 and 19. He would have had to cut off, he would have had to cut off all of this right over here in order to get it down to 19. So much would he have to cut off? Well this right over here is going to be 36 minus 19. It's the difference between 36 and 19. So let's figure out what that is. It's going to be 36 minus 19. So let's see, if we... we have six ones, we want to take away nine ones. So let's do a little bit of regrouping. Let's take one of our 10s here, so instead of three 10s, we have two 10s. And then if we add that 10 to the ones place, instead of six ones, we're gonna have 16 ones. 16 minus nine is seven. Two 10s minus one 10 is one 10. So he would have had to cut off 17 centimeters of his scarf. If he started with 36 centimeters, he cuts off 17 centimeters, he's going to be left with 19 centimeters. And you could do that the other way around. You could start with 36, you could cut 17, and see what you end up with. You're going to see that you end up with 19.