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mrs. Henry's class has 64 crayons at the end of the year only 31 crayons remain how many crayons have been used and they give us a picture here so at the beginning of the year this is 64 crayons six tens and four ones one two three four five six tens and one two three four ones so this is 64 at the beginning of the year and at the end of the year only 31 crayons remain well 31 is three tens and one one three tens 1/10 2/10 3/10 and one one so how many have been used and try to pause the video and try it on your own all right I assume you have tried it let's do it together so there's a couple of ways to do it if we didn't have the picture here we would say all right she started her class started with 64 crayons they used some so for your using crayons that would kind of subtract the crayons away so if you're using some crayons you would subtract some number from 64 so I'm just going to put a blank here so 64 minus the number that are used is going to be equal to the number that remain so this is going to be equal to what's left over they tell us that 31 crayon germain 31 crayons remain so we assent we need to figure out what's here what is this blank 64 minus blank is 31 well 64 minus blank is 31 then I can swap the 31 and the blank that means that 64 that means that 64 minus 31 is going to be equal to blank that means that 64 minus 31 - 31 is going to be equal is going to be equal to blank how did I do that how do I think about that well imagine 64 things so this is if this block represents 64 so this is 64 just like that and if this is 31 if this is 31 and then this is our blank this is our blank we know that the blank so this is I could put a question mark here if I like I could put a question mark so this is the question mark so we know that 64 minus the question mark would be 31 or the 31 plus question mark would be 64 or that 64 minus 31 is going to get us the question mark right over here so we just have to figure out what 64 minus 31 is and let's do that let's do that right over here so 64 minus 31 - 31 and it's going to be equal to so let's look at the ones place four ones minus one one is going to be three ones six tens minus three tens is three tens so the blank is 33 and you could check that 64 minus 33 is 31 or 64 minus 31 is 33 so 33 crayons have been used now since they made this neat picture for us we actually could have just used the picture how would we have done that well this is what they started with this is the sixty-four six tens one two three four five six tens and one two three four ones so 64 and they end up with 31 so how many of the tens do we use up to go from what we started with to what we finish with well we end up using let's see there's only three tens here there were six tens here so we used one two three tens so we used up three tens and how many ones do we use up well we have four ones here and we only have one right over here so we use up three ones we used up three ones if you take away these three tens and these three ones you'll be left with the same number of crayons that we have at the end of the year so we use up three I guess you could say we used up three ten packs and we used up three ones so what's that going to be well three tens plus three ones is is 33