Class 2 math (India)
Sal solves a subtraction word problem with numbers less than 100.
- After Thursday's snow storm, the snow in Chillytown was 55 centimeters deep. On Friday, the snow kept coming and several more centimeters fell. So, okay, they're getting a lot of snow. Now, the snow in Chillytown is 84, 84 centimeters deep. How many centimeters of snow fell on Friday? So let's look look at this diagram again, just so that we can imagine what went on. So, the first time... So the snow in Chillytown... There's a storm on Thursday, and then the show in Chillytown was 55 centimeters deep and they show that to us right over here. So this is the 55 centimeters, is this point on the ruler. So this is how deep, this is how deep the snow was after the storm, after the storm on Thursday. This is how deep. So this depth right over here is 55 centimeters. But the snow did not stop, it kept coming. So now the snow in Chillytown is 84 centimeters deep. So in the ruler, that's this right over here, 84 centimeters deep. So they wanna know how many centimeters of snow fell on Friday. So they want us to figure out what is this amount right over here? What is the amount that fell on Friday? They even put the question mark right over here. Question mark centimeters. So how do we figure that out? Well, let's just right some... Let's write some things that we know are true. So we know that 55 centimeters... 55 centimeters, plus however many centimeters this was, so I'll write question centimeters. So this is how many were after Thursday's snow storm, plus however many fell on Friday. We don't know that, so I'm just gonna write a question mark over there. That's going to be equal to the total. That's equal to 84 centimeters. That's equal to 84 centimeters. So we just need to figure out what's this question mark. Well, one way to figure out what this question mark is if 55 plus question mark is 84, then that means, that means that 84 minus 55, minus 55 is going to be equal to the question mark, is going to be equal to the question mark. And one way to think about it is, if you had all this snow and you were to subtract out 55 centimeters of it, you're just going to be left with the question mark amount because the difference between 84 and 55 is what fell on Friday. The difference between 84 and 55. So let's figure out what that is. So I can do that. I'm running out of space here, I'll do it down here. So we have 84, 84 minus 55, minus 55, and that's going to be equal to our question mark. So let's look at our ones place. We have four ones minus five ones. Well, since we don't know how to do that, since four is less than five, so let's regroup. So let's take a 10 from the 10s place. Instead of having eight 10s there, let's have seven 10s there and then make that extra 10 we just took, turn that into 10 ones. So 10 plus four is 14. So now we can subtract. 14 ones minus five ones. Let me move down a little bit. 14 ones minus five ones is nine ones. Seven 10s minus five 10s is two 10s. So our mystery amount of snow, 29 centimeters. So this right over here is 29 centimeters. And you can check that. 55 plus 29 is indeed equal to 84. I encourage you to try to check that that does definitely work. So how many centimeters of snow fell on Friday? 29, 29 centimeters. The important thing for problems like this is just imagine the story. Imagine what's going on, and then draw diagrams if they didn't draw it for you, and then think about writing some math statements. Some people would call them number sentences or equations that you know are going to be true and then you can figure out what you don't know.