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Mathematics 19 Online
OpenStudy (highschoolmom2010):

The surface areas of two similar figures are given. The volume of the larger figure is given. Find the volume of the smaller figure.

OpenStudy (highschoolmom2010):

OpenStudy (anonymous):

what is figure? is it sphere?

OpenStudy (highschoolmom2010):

it was not specified

OpenStudy (phi):

use the same idea as the last problem. first find the ratio of their "sides" (i.e. the square root of the ratio of their surface areas) then cube that ratio to get the ratio of volumes.

OpenStudy (dan815):

doesnt this only work if it happens to be a cuve tho

OpenStudy (highschoolmom2010):

\[\frac{ \sqrt52 }{ \sqrt192 }\]

OpenStudy (phi):

@dan815 amazingly it works for any *similar volumes*

OpenStudy (dan815):

ya i know it doesnt work for cube

OpenStudy (highschoolmom2010):

now i am confused

OpenStudy (phi):

for a cube of side=1, its surface area is 6 cube side= 2, its surface area is 24 ratio of surface areas is 6/24 = ¼ square root gives us ½ ( the ratio of their lengths) cube ½ to get ⅛ ratio of their volumes

OpenStudy (phi):

@highschoolmom2010 you are on the right track...

OpenStudy (phi):

Sorry, dan was wrong, not highschoolmom

OpenStudy (highschoolmom2010):

oh ok

OpenStudy (phi):

except you want the ratio of surface areas... in other words 52/208 that you take the square root of.

OpenStudy (highschoolmom2010):

oh ok

OpenStudy (highschoolmom2010):

\[\frac{ \sqrt52 }{\sqrt 208 }=\frac{ 1 }{ 2 }\]

OpenStudy (phi):

now cube that ratio to find the ratio of their volumes.

OpenStudy (highschoolmom2010):

\[\frac{ 1^3 }{ 2^3 }=\frac{ 1 }{ 27 }\]

OpenStudy (dan815):

it works for spheres too but, its hard to see, how can it work for any sorface and volume possible

OpenStudy (highschoolmom2010):

\[\frac{ x }{ 52 }=\frac{ 1 }{ 27 }\]

OpenStudy (dan815):

is it because technically any volume can be broken down into a sum of little cubes

OpenStudy (phi):

½ cubed is not 1/27 ½ * ½ * ½ = ?

OpenStudy (highschoolmom2010):

oh ok

OpenStudy (highschoolmom2010):

\[1/8\]

OpenStudy (phi):

yes, now set up your ratio of volumes

OpenStudy (highschoolmom2010):

\[\frac{ x }{ 52 }*52=\frac{ 1 }{ 8 }*52\]

OpenStudy (phi):

where did you get 52 ?

OpenStudy (highschoolmom2010):

for the original question

OpenStudy (highschoolmom2010):

wait i see

OpenStudy (highschoolmom2010):

\[\frac{ x }{ 192 }*192=\frac{ 1 }{ 8 }*192\]

OpenStudy (phi):

much better!

OpenStudy (highschoolmom2010):

X=24

OpenStudy (phi):

looks good.

OpenStudy (highschoolmom2010):

hooray thanks @phi @dan815

OpenStudy (dan815):

suer

OpenStudy (dan815):

=]

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