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Addition and subtraction word problems: gorillas

CCSS.Math: , ,

Video transcript

there were some guerrillas lifting weights in the gym then three more guerrillas came and started running now 17 guerrillas are in the gym how many gorillas were lifting weights so that's the number of gorillas that were originally in the gym the gorillas lifting weights so how many gorillas were lifting weights and they have this diagram for so what is this diagram telling us how many squares are there there's 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 squares so this 17 this is how many gorillas there are now in the gym so this is the 17 right over here how many gorillas how many gorillas there are now in the gym how many gorillas there are now in the gym that's the 17 now there were some gorillas in the gym three more came and started running so maybe these are the three that came in and started running so 1 2 3 so how many were there to begin with how many there were there lifting weights so all the rest of these must have been there lifting weights so that is 1 2 3 4 5 6 7 8 9 10 11 12 13 14 so 14 gorillas were lifting weights that's the ones where I wrote the numbers in this in this purplish color then three more came came in and started running and now there are 70 and you see the 17 block so how many gorillas were lifting weights to begin with well that's the 14 that is that is the 14 and there's other ways that you could have done this you could have said okay there were some number of gorillas that were lifting weights in the gym now three more gorillas walk in three more girls walk in and now they're going to be they're now going to be 17 gorillas so you could say okay something plus 3 is 17 or you could say 17 minus 3 minus the 3 that walked in well that's going to give you how many you originally had how many you originally had and either way you think of you're going to get to you are going to get to 14 17-3 you could view that as well this 17 is one 10 and 7 ones so you take away three ones 7 minus 3 is 4 so 17 minus 3 is going to be 14 let's do another one of these and this is more of what you might see on Khan Academy and it's good to just know what they're asking for so this says I bought a bag of 13 mini chocolate chip cookies my sister ate some of them and I was left with 8 cookies and I was left with 8 cookies how many cookies did my sister eat so I had a bag of 13 cookies I had a bag of 13 cookies my sister ate some of them so those cookies are going away so I'm going to subtract those cookies so my sister ate some of them so that's the question mark how many cookies did my sister eat she ate some of them and then I was left with eight cookies and then I was left with eight cookies so 13 minus something is equal to eight or you could view this as if you want to solve for the something you could say the 13 and some of you might just say okay I know 13 minus 5 is equal to 8 so you'd know that the question mark is equal to 5 or you could say that 13 13 minus 8 minus 8 is equal to question mark is equal to question mark or you could even say well if I was left with 8 cookies you could say if I was left with 8 cookies and my sister ate some of them so this is what I left with Plus this one's that my sister ate that must be how many cookies I originally had that must be the number of cookies I originally had so any way you do it you get your question mark is equal to 5 sister ate 5 cookies now they asked us which choices can help you solve the problem well all of these this is so now we know the question mark is 5 we know that 13 minus 5 is equal to 8 so let me write that down we know that actually let me just replace this let me just replace this with a 5 so 13 minus 5 is equal to 8 well that's a true statement that's describing what just happened here so this could help me or actually not that one that's 13 plus 5 13 minus 5 equally 8 that's this right over here and that is a useful thing to know because look if I started with 13 cookies my sister ate five Oh might be left with eight now what about this one over here 13 minus 8 well we know this would be equal to five now but they don't have a 13 minus 8 equals 5 so we want to select that and then here we now know question mark is 5 so 8 plus 5 is 13 8 plus 5 is 13 that's useful too because we know 8 plus 5 is 13 then we know what I'm left with plus what my sister ate is 5 is going to be the 13 that I started with 13 plus 5 equals 18 not so useful 18 has nothing to do with the problem there were no somehow it's not like my sister somehow baked five more cookies and added them and now I'm left with 18 cookies I'm left with eight cookies now and so I didn't add the five she ate those cookies so I would subtract them