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Current time:0:00Total duration:2:47

Worked example: Subtracting 3-digit numbers (regrouping)

CCSS.Math: ,

Video transcript

let's try to subtract 659 from 971 and as soon as you start trying to do it you face a problem you go to the ones place and you say how am I going to subtract a nine from a one and the answer lies in regrouping taking value from one of the other places here and giving it to the ones place and to understand that a little bit better let me rewrite these two numbers let me expand it out so this nine is in the hundreds place so it represents 900 the 7 is in the tens place so it represents seven tens and then this one is in the ones place so it just represents 1 and then down here this six represents 600 600 this five represents five tens or fifty and then this nine will still just represents nine 1s or nine and we're subtracting this we're subtracting 600 plus 50 plus nine or another way of thinking about it we're subtracting 600 we're subtracting 50 we are subtracting nine so let's work it out over here so this is the exact same problem just written a little different bit differently and we still have the same issue how do we subtract a larger number from a smaller number and the solution lies in trying to take value from one of the other places and the easiest place to go is look look we've got 70 here why don't we take 10 from here and we'll be left with 60 and give that 10 to the ones place so if you add 10 to one what do we have well then we're going to have we're going to have 11 notice I have not changed the value of the number 971 is the same thing as 900 plus 60 plus 11 it's still 971 and now we can actually subtract 11 minus 9 11 minus 9 is 260 minus 50 is 10 and 900 minus 600 is 300 is 300 so this this this subtraction should result in 300 plus 10 plus 2 which is 312 now let's do the exact same thing here but we're going to do it using without expanding it so the same issue how do we subtract a nine from a one well let's take a 10 from the tens place we're gonna regroup so we're gonna get rid of one of these 10 so we're all gonna have six tens left in the tens place and we're gonna give that 10 to the ones place so 10 plus 1 is 11 now we are ready to subtract 11 minus 9 is 2 6 minus 5 is 1 9 minus 6 is 3 we get let me do that same color we get 312