Sal solves 1 addition and 1 subtraction word problem.
- Fourteen superheroes met on the moon for a top secret gathering. Fascinating. Three of them turned out to be evil villains in disguise. Uh oh. How many were real superheroes? Real superheroes. So pause this video and see if you can figure this out. Now you've had your try, let's work on it together. So fourteen superheroes met on the moon. So let's write that down. Fourteen met on the moon. I'll put a little circle around it like that. So fourteen met on the moon. Now of that fourteen, they tell us that three of them turned out to be evil villains in disguise. So three of them are evil villains. So of the fourteen, we're either dealing with the three evil villains, or we're dealing with real superheroes. One way to think about it is the fourteen are made up of evil villains or real superheroes. So this question mark right over here, this is the real superheroes. This is what we need to figure out. And so this relationship could be written in different ways. You could write... You could write that the three villains plus the question mark, real superheroes, plus the question mark, real superheroes, is going to be equal to the total number of characters that met on the moon. Or you could say, well if three plus question mark is fourteen, well then fourteen minus three, minus three, is going to be equal to question mark. Is going to be equal to question mark. And you see it right over here. The fourteen is made up of three and question mark. So if you take fourteen minus three, you're just going to be left with the number of real superheroes. So what's fourteen minus three? Well, there's several ways you could do this. But one way is, let's see, fourteen minus one is going to be thirteen. Fourteen minus two is twelve. Fourteen minus three is eleven. So we have eleven is equal... Eleven is equal to question mark. Or question mark is equal to eleven, or there are eleven real superheroes. Now let's do one more. Let's do one more. We found many sea monsters in the nearby lake. Nine of them have stripes. Five of them have spots. How many sea monsters are in the lake? How many sea monsters are in the lake? So what are they telling us? So the total... How many sea monsters in the lake? This is the total number of sea monsters. This is what we're trying to figure out, the total number of sea monsters. That's how many sea monsters are in the lake. And they tell us, they tell us that nine of them have stripes. Nine of them have stripes. And five of them have spots. Five of them have spots. So all of the sea monsters are going to be the nine that have stripes, plus the five that have spots. So we could write nine plus five. Nine plus five is equal to question mark. Is equal to question mark. And so what is nine plus five? Well you might have that memorized already. That is fourteen. Or if you don't, you could see say, well let's see. Nine plus one is going to be ten. Nine plus two is eleven, nine plus three is twelve, nine plus four is thirteen, nine plus five is fourteen. So you have fourteen is equal to question mark. Or how many sea monsters are in the lake? Fourteen.