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Mathematics 17 Online
OpenStudy (anonymous):

Three tennis balls are packed tightly in a rectangular box. What is the ratio of the volume of the tennis balls to the volume of the box?

jimthompson5910 (jim_thompson5910):

It's not 100% clear, but I'm assuming the tennis balls are packed like this |dw:1399874375587:dw|

jimthompson5910 (jim_thompson5910):

it's not drawn perfectly since the 3 tennis balls are supposed to touch

jimthompson5910 (jim_thompson5910):

anyways, let's say the diameter of one ball is 1 unit |dw:1399874441199:dw| what would be the length of the rectangle?

OpenStudy (anonymous):

Yes thats what it looks like. The length of the rectangle would be 3

jimthompson5910 (jim_thompson5910):

good

jimthompson5910 (jim_thompson5910):

what is the width of the rectangle?

OpenStudy (anonymous):

1

jimthompson5910 (jim_thompson5910):

correct

jimthompson5910 (jim_thompson5910):

what is the height of the box?

OpenStudy (anonymous):

Isn't the height the same as the length? so 3?

jimthompson5910 (jim_thompson5910):

not quite

jimthompson5910 (jim_thompson5910):

imagine we have this 3D box |dw:1399874761408:dw|

jimthompson5910 (jim_thompson5910):

we found the length and width so far |dw:1399874790789:dw|

jimthompson5910 (jim_thompson5910):

the height is the same as the diameter of each ball (to make sure they fit in terms of the height), so the height is 1

jimthompson5910 (jim_thompson5910):

|dw:1399874819427:dw|

OpenStudy (anonymous):

Okay, that makes sense

jimthompson5910 (jim_thompson5910):

what is the volume of that rectangular box?

OpenStudy (anonymous):

The volume is 3

jimthompson5910 (jim_thompson5910):

3 cubic units, good

jimthompson5910 (jim_thompson5910):

if a sphere has a diameter of 1, what is the volume of that sphere?

OpenStudy (anonymous):

4.2 cubic units?

jimthompson5910 (jim_thompson5910):

If you used the formula V = (4/3)*pi*r^3 then you are correct

jimthompson5910 (jim_thompson5910):

but remember the diameter is 1, so the radius would be half that: 1/2 = 0.5

jimthompson5910 (jim_thompson5910):

so you should have V = (4/3)*pi*(0.5)^3 V = ??

OpenStudy (anonymous):

Oh yeah thats right, so the volume is actually .524. But since there is three of them we times it by 3?

jimthompson5910 (jim_thompson5910):

I'm getting 0.5235987755983, so it looks like you got it

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