Sal adds fruit and subtracts fruit. The examples he uses are 5+3 and 5-3. Created by Sal Khan.
Voiceover:We have one, two, three, four, five blueberries here, so we have five blueberries, and we have one, two, three cherries, three cherries. Now, if I wanted to figure out the total number of fruit that I have here, I could say the total number of pieces of fruit, what should I do? Should I add five plus three? So, should I add five plus three, or should I subtract? Should I do five minus three, to get the total number of fruit that I have? I encourage you to pause the video now, and try to think about it on your own. If I want the total number of fruit, I'm starting with five blueberries, and now I have three more. I'm going to add three. I'm going to get a larger number of fruit. I start with five; I'm going to have three more, so I am going to add three, and so, how many blueberries do I have? What's five plus three? It's one, two, three, four, five, six, seven, eight pieces of fruit. Eight pieces of fruit. Now, what would five minus three have meant? What would five minus three, five minus three, what would that mean? You can imagine starting off with five pieces of fruit, let me copy and paste that, copy and paste that, so, if you start with five pieces of fruit, and now if you're subtracting three, this means taking away three of your fruit, so take away one, take away two, and take away three, so how many are you left with? You're just left with these, one, two, right over here, so five minus three is two. If someone says, "Hey, I have five blueberries, "and then I have three more cherries, "how many pieces of fruit?" well, now I'm going to be adding. If someone says, "I have five blueberries, "and then I ate three of them, "how many do I have left?" well, then you have two left.