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Current time:0:00Total duration:2:32

Video transcript

what I want you to do is pause the video and think about what 27 minus 1 is and then think about what 27 minus 10 is all right you might have found it pretty straightforward but I want to think about it in terms of place value so let's focus on 27 so 27 I have 2 in the tens place so that 2 means two tens and we see them here to groups of 10 and then we have seven in the ones place and we see those seven ones right over here now I'm going to subtract one I'm subtracting one one is another way to think about it because this is in the ones place here so I'm going to take away one so let's just take away one like that and then what am I left with well I still have my two tens so I could put a two in the tens place so I still have a two in the tens place and now how many ones do I have well I used to have seven I took one away now I have six ones so now I have six ones so two tens and six ones well we can call that 26 now let's think about 27 minus 10 so once again this is 27 two tens and 7 ones and now we're not going to take away anyone's but we're going to take away 110 let's just remind ourselves a 10 is literally 1 to n I know that sounds like I'm saying the same thing over and over again but I really want you to appreciate the place value this is the tens place and I have a 1 there so I'm going to take away 1 10 and 0 ones so let's take away that 10 so let's take away maybe I'll take this one away I'll do it in a color that's easier to see see so I could take that away and then what am I left with how many tens am I left with well I only have one full group of 10 so I have 1 10 so that's the tens place right over there and how many ones do I have well I still have seven ones so I still have seven in the ones place so 27 minus 10 is 1 10 and 7 ones or 17 and another way that you could think about it and this might be the way that you did it when I first asked you to do it hey if I'm taking away a one I'm going to I'm going to reduce my ones place by one so I go from 27 to 26 but if I'm taking away a 10 then my tens place is going to go down by one so I go from a two in the tens place to a 1 in the tens place I go from 27 to 17 the ones place didn't change