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Current time:0:00Total duration:3:22

Transitioning from unit squares to area formula

CCSS.Math: ,

Video transcript

this square is one square unit so what is the area of rectangle a the first thing we're told is that each of these little squares equal one square unit and then we're asked to find the area of rectangle a here's rectangle a an area is the space that it covers so how much space does rectangle a cover how many square units does rectangle a cover one way to answer that would be to count how many square units it covers except they've covered up our square units so one idea is we could draw them back say you cover them up we'll draw them back in so going like this connect all these and then we should be able to count our square units so we have one two three four five six seven eight nine ten eleven twelve twelve square units rectangle a covers 12 square units so it has an area of 12 square units but this isn't the only way that we could have solved this we could have also said we could have also looked at this and said okay this top row is 4 square units long 1 2 3 4 has a length of 4 units so that means the top row will have 1 2 3 4 square units inside of it and then we could have looked over on the side over here and said well how many rows of four will they'll be it'll be 1 2 3 rows of 4 so we'll have this row of 4 and then a second row of 4 and a third so 3 times we will have 4 square units there's 4 square units at the top another in the middle and another at the bottom 3 times we will have 4 square units or we could go and farther than that so we could have said we could have done three times four or we could look at this and say okay here's one column this column has three square units it has a length of three one two three how many of these columns like this will there be it'll be one two three four because our length here up at the top is four so this time four times we will see three square units one two three and we'll see that one two three four times so no matter which of these we solved whether we counted the square units like in the beginning or we multiplied the side lengths the three and the four in every case we're going to find that this equals twelve square units the area of rectangle a is twelve square units because it covers twelve square units