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Current time:0:00Total duration:4:27

Video transcript

all right so we have ying-ying had run a total of 30 laps for running class or a running club I should say so yang Ying ran a total of 30 laps then Ying Ying ran 4 more laps before school so she ran 4 more laps before school three more laps at lunch three more laps at lunch and two more laps at recess Ying Ying's doing a lot of running two more laps at recess so what I want to do is I want to figure out the total number of laps that Ying Ying ran and I'm going to do it using a number line so let's draw a number line here let's draw a number line let's draw a number line and Ying Ying starts at 30 laps she had run 30 laps and then she keeps reading she keeps running more laps than that so my number line I could start it wherever I want but it might be convenient to start it at 30 and it obviously could I could do it at 29 and then I could go 30 actually let me just keep going up from there 31 32 33 34 35 a few more left 36 37 38 39 and let's say 40 and I could go all the way to 41 that's how much space I have so let's see Ying Ying started at 30 laps so she started at 30 laps for a running club then she ran Ying Ying your aunt four more laps before school so on the number line if I go four more that's going to be to the right I'm going to be increasing by four so I'm going to be increasing by one two three four so those four laps before school take us from thirty to thirty four then she rat and runs three more laps at lunch so then from the 34 she's going to go one two three to 37 it's going to go to 37 so that's what those three more laps at lunch do for us and then two more laps at recess so she was at 37 and now we're going to go one to 2:39 so how many total laps does ying-ying run well ying-ying runs a total of 39 laps 39 laps and we were able to figure it out using this number line now let's do a an exercise very similar to this that you might see on Khan Academy so this one right over here she'll be get rid of the stuff about ying-ying so we don't get confused so this says and it's a little bit smaller but hopefully you can see what it says a red ant army started with 100 started with 100 marching ants so we're going to start with 100 and actually they tell us well let me just read the whole thing started with 100 marching ants then the Red Army lost 3 ants down a hole so actually let me let me get it so lost 3 ants down a hole 3 ants we're eaten by a bird that's unfortunate and one ant just blew away I guess ants are fairly light creatures so that makes sense one ant blew away which number line shows how to find how many ants the Red Army has left well the army started with 100 marching ants we underlined that over here so we need to start with 100 so we need to start with 100 this one starts with 10 so I can immediately rule this one out and so we could just we could just select that one but let's just make sure it makes sense so we start with 100 and then we lose 3 ants down a hole so we're going to go down remember we're losing ants so we're going to go to the left of the number line we're gonna go to lower values we're going to go down 1 2 3 so these are the 3 ants we lose down a hole so 3 down the hole then we have three that we're eaten by a bird so you're going to lose 3 more that's those three right over there goes to 94 ants left and then we have the one ant that gets blown away so that gets us down to 93 ants left so the Red Army or the red ant army has 93 ants left 93 93 ants left and we are done