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Video transcript

let's see how we could approach 4 and 1/4 minus 2 and 2 for its pause this video and have a go at that before we work on this together alright so the first thing that you might try to do is rewrite this as 4 and 1/4 minus 2 and 2/4 and the reason why it's useful to write it this way is we could say look each of these mixed numbers have a whole number part and then they have a fractional part and so I could try to subtract the fractional part from the fractional part and then the whole number part from the whole number part and that will often work but when we go to just the fractional parts and we say hey how do I subtract two forts from one-fourth two-fourths is larger than 1/4 you immediately might find yourself in something of a conundrum so what do you do well what comes to the rescue is a notion called regrouping and that's that we're not just subtracting 2/4 from 1/4 we're subtracting 2 and 2/4 from 4 and 1/4 so what we could do is we could take some of the value that's in this 4 and regroup it into the fraction what do I mean by that well instead of 4 if I view for as 3 and 4/4 4/4 and so 4/4 plus 1/4 is 5/4 5/4 so I can rewrite this as 3 and 5 fourths minus 2 and 2/4 once again why is that useful because 5/4 is greater than 2/4 what is 5/4 - 2/4 well that's going to be 3/4 and then what is 3 - 2 well that's going to be 1 and we get 1 and 3/4 another way we could have thought about it is this is the same thing as 4 minus 2 plus 1/4 plus 1/4 minus 2/4 - 2/4 and we have trouble with the 1/4 minus 2/4 that's what we saw right over here so what we do is we take some of that value from the 4 instead of 4 we could rewrite that as three plus four fourths that's the same thing as four and of course you have minus two plus 1/4 minus two fourths and then if you add the 4/4 to the 1/4 that's going to give us five fourths so you're going to have three minus two that's that part in that part and then you're going to have if you add the four fourths and the 1/4 so plus five fourths minus two forts and that's exactly what we have here three and five fourths three and five fourths minus two minus two and minus two fourths and so 3 minus 2 is 1 five fourths minus two fourths is three fourths