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Mathematics 6 Online
OpenStudy (loganator):

MEDAL + FAN Please help What is the surface area of the composite figure? Photo is attached 256 cm^2 384 cm^2 512 cm ^2 544 cm^2

OpenStudy (loganator):

OpenStudy (solomonzelman):

Can you re-write the choices in numbers?

OpenStudy (loganator):

ok

OpenStudy (loganator):

Done

OpenStudy (solomonzelman):

And I will show you how to do it. You have 2 rectangles BOTTOM: 4 on 4 on 8 TOP: 4 on 4 on 24

OpenStudy (loganator):

or one rectangle 2 cubes :/

OpenStudy (solomonzelman):

You have 2 'cubic' rectangles. I mean 3D rectangles.

OpenStudy (loganator):

yes 1 rectangular prism 2 cubes

OpenStudy (solomonzelman):

Ohh, wait you are looking for surface Area, so I am incorrect.

OpenStudy (loganator):

you also must subtract interior faces, I did everything and got something like 575

OpenStudy (solomonzelman):

Wait, I can only count the faces that I can see, but not all of them ?

OpenStudy (loganator):

OHHHHHHHHHHH wait I see what I did wrong

OpenStudy (loganator):

you see you split up the figure into smaller figures, when you do that, extra faces become visible that aren't going to be covered in the actual equation, so you have to kind of subtract those from the actual area

OpenStudy (loganator):

there are 4 interior faces I missed thats why my answer came out wrong

OpenStudy (solomonzelman):

yes, but first, I am trying to find all faces of two rectangles as if they are separate, and then subtract the faces they have in common.

OpenStudy (solomonzelman):

And you are right, the only face that is not actually there is the 4 by 4 face.

OpenStudy (loganator):

yeah but when the 4 by 4 faces connect there are actually 2 4 by 4 areas you have to subtract, and the 4 by 4 face on the top

OpenStudy (loganator):

So the answer is actually 544

OpenStudy (loganator):

so when you add the surface area for all of the 3d figures up you get 608, but 608 - 16 - 16 - 16 - 16 = 544 :)

OpenStudy (solomonzelman):

BOTTOM rectangle: 4 on 4 on 8 TOP rectangle: 4 on 4 on 24 then the face 4 by 4 is 16. bottom rectangle: 2(4×4)+2(4×4)+2(4×8) top rectangle: 2(4×4)+2(4×4)+2(4×24)    ──────────── 4(4×4) + 4(4×4) + 2(4×8) + 2(4×24) 4(4×4) + 4(4×4) + 2(4×8) + 2(4×8×3) 4(4×4) + 4(4×4) + 2(4×8) + 6(4×8) 4(4×4) + 4(4×4) + 8(4×8) 4(4×4) + 4(4×4) + 8(4×4× 2) 4(4×4) + 4(4×4) + 16(4×4) (4+4+16)(4×4) (24)(4×4)

OpenStudy (solomonzelman):

There are 24 '4 by 4' faces.

OpenStudy (solomonzelman):

Subtract 1 4 by 4 face that is not actually there. you get `23(4 × 4)` and the exact answer is 368.

OpenStudy (loganator):

Well technically thats not in my answer choices

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