Find the surface area of the prism.

Question

anonymous · Answer

attachment

hartnn · Answer

find the area of its six surfaces

anonymous · Answer

How do I do that? @hartnn

mathmale · Answer

First, what's the formula for the area of a rectangle of length L and width W?

anonymous · Answer

Length x width? @hartnn

hartnn · Answer

each surface is a rectangle surface.

Area of rectangle is ...

hartnn · Answer

yes

anonymous · Answer

65, right @hartnn

hartnn · Answer

if you want the ready-made formula:
$A_{surface-prism} =2 (lw+wh+hl) $

l = length
w = width
h = height

hartnn · Answer

65 is area of just one face, isn't it?

anonymous · Answer

I just did 13 x 5. l x h @hartnn

hartnn · Answer

yes, 
what aboout other 5 faces?

mathmale · Answer

think of the matter in this way:  Your figure has two tops, two sides and two ends.

Area of 1 side is 65 square inches.
What's the area of the other side?

Area of one end is .... ?
Sum of areas of both ends is ... ?

Area of top, times two, is... ?

anonymous · Answer

Do I have to do 13 x 6 to? @mathmale @hartnn

hartnn · Answer

yes
thats the area of one more face

anonymous · Answer

That would be 78... @hartnn

mathmale · Answer

"Do I have to find the area of the bottom, by multiplying 6 m and 13 m?"  Yes, you do.

mathmale · Answer

If the area of the bottom is 78 sq. meters, what's the area of the top?

hartnn · Answer

as of now, you have areas of 4 faces,

2 faces having area 13*6  = 78 each
2 faces having area 13*5 = 65 each 

2 more faces to go!

anonymous · Answer

Do you divide 78 by 65 next? @hartnn @mathmale

mathmale · Answer

Think:  Why are you proposing division?

mathmale · Answer

Area is a product:  L * W.

hartnn · Answer

why divide? 

we will add all the areas of 6 faces to get the total area

anonymous · Answer

Oh, I just thought sense its the opposite of multiplying.

hartnn · Answer

what is the area of side faces having length = 5 width = 6 ?

anonymous · Answer

is that 5x6 @hartnn

hartnn · Answer

yes!

anonymous · Answer

Ok then, 30 @hartnn

hartnn · Answer

so add up all the six areas now

hartnn · Answer

2 faces having area 13*6  = 78 each
2 faces having area 13*5  = 65 each
2 faces having area 5*6  = 30 each

anonymous · Answer

So add 78, 65, and 30? @hartnn

hartnn · Answer

add them twice, because there are 2 surfaces of those areas each

mathmale · Answer

But aren't there TWO of each the end, the top, the side?

hartnn · Answer

78+78+65+65+30+30
^^

anonymous · Answer

346 @hartnn

hartnn · Answer

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