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Current time:0:00Total duration:3:40

CC Math: 7.EE.B.3

Joelle is working on a school
report in a word processor. She wants to place a figure
which is 13.09 centimeters wide so that it appears
centered on the page. The width of the page
is 21.59 centimeters. How much margin should
she leave on the left so that the figure is centered? So let's visualize
what's going on. We have a page that's
21.59 centimeters wide. So this distance right over
here is 21.59 centimeters. So this right over
here, that is our page. Let me draw the actual page. Let me draw that in white,
since paper tends to be white. So this is her page. It's 21.59 centimeters wide. It's just like that. It's a little unusual
dimension for a piece of paper. But we'll go with it. And then she wants to
place a figure that is 13.09 centimeters wide
in the center of the page. So the figure-- I'll
do it in magenta. That's not magenta. The figure is 13.09 centimeters. So let's say that this is
the figure right over here. So this is the
figure that she wants to place in the
middle of the page. So this is 13.09 centimeters. So the question is, how
much margin should she leave on the left so that
the figure is centered? So they're really asking,
what should this distance be here so that the
figure is centered? And the key thing is, if
the figure is centered, this distance is going to be
the same as this distance, so that the figure is
right in the middle. Whatever this is, it's going
to be the same as this. So one way we could
think about it-- we could say, OK, let's take
13.09 centimeters from 21.59 centimeters. And if we do that,
then we'll know how much leftover space
this plus this combined is. And then we just want to
split that space in half. We want half of it to
go on the right side, and we want half of it
to go on the left side. So let's see how much this left
margin and the right margin combined need to be. And that's just 21.59. That's just going to be
21.59 centimeters minus 13.09 centimeters. And this, we get to-- let's see. This is 8.50 centimeters,
which is the combined margins. Not just the left or
not just the right-- this is the left plus the right
margin, is 8.50 centimeters. This is this distance
plus this distance. Now, if we want to figure out
what the left margin should be, if we want to center it. Well, we just want
to split this evenly between the left and
the right margin. So we just want to
divide this by 2. So if you divide 18.50 by 2--
or multiply it by 1/2, I guess. That might be a little bit
more obvious-- either way. So if we multiply this by 1/2,
you are left with 1/2 of 8.50, is 4.25 centimeters. So if we want it
centered, this is going to be 4.25 centimeters. And of course, this is going to
be 4.25 centimeters, as well. And you see, when
you add 4.25 to 4.25, you get 8.5 centimeters. And then you add that to 13.09. You get the entire width
of the piece of paper. So how much margin should
she leave on the left? 4.25 centimeters.