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CCSS.Math:

we are told a teacher bought 12 sheets of stickers to use on the homework of her students each sheet had 48 stickers at the end of the year the teacher had 123 stickers remaining which is the best estimate for the number of stickers the teacher used so like always pause this video and see if you could have a go at this before we work on this together alright now let's work on this together so the first thing to appreciate is we just have to figure out an estimate we don't have to figure out the exact number of the stickers that were used let's see if we can do that so let's see we have 12 sheets of stickers and each sheet had 48 stickers 48 stickers per sheet so how many stickers did the teacher start off with well there were 12 sheets times the number of stickers per sheet so times 48 times 48 this is going to be the number that they started off with number to start and then if we want to figure out the number that are used we just have to figure out okay from the number that was started how many are left over and then that's how many were used and so how many were left were left over well 123 were remaining at the end of the year so that's this number right over here so if we calculate that first the number to start we subtract out the number that are remaining then that will be equal to the number of stickers that the teacher used now once again we don't have to figure out exactly we just have to estimate and so I'm just going to try to figure out friendlier numbers to work with so instead of 12 let's imagine let's imagine actually I'll stick with 12 12 I can work with but let's say that this is going to be approximately equal to so in parenthesis instead of 48 I'll say it's roughly 50 so this is going to be approximately 12 times 50 instead of 123 I'll say that's roughly a friendlier number might be a hundred and twenty or might be a hundred that's just 220 so minus 100 we could have done a hundred and so we could figure out what this is in our heads or with a little bit of paper 12 times 5 is 60 so 12 times 50 is 600 and then 600 if we had a hundred-year 600 minus 100 movement at 500 or 600 minus 120 is 480 so what we want to do is look in the choice and see which of these choices is closest to roughly 500 or roughly 480 and so let's see out of all of these actually they have exactly 480 which is so they estimated exactly the way we happen to estimate now not every person is going to do that we could have two chosen instead of hundred 23 becoming 120 in our estimate we could have put a hundred there and then we would have gotten 500 but even if 500 was our estimate 480 still would have been the closest to that estimate