# volume and surface area

• Jun 24th 2009, 08:19 AM
andyboy179
volume and surface area
i need to know how to work out the volum and surface area of this shape, if you know how to please post:

Attachment 11980
• Jun 24th 2009, 08:21 AM
Unenlightened
Quote:

Originally Posted by andyboy179
i need to know how to work out the volum and surface area of this shape, if you know how to please post:

Attachment 11980

How much of this type of stuff have you done in school?
Could you get the area of a square, if you were given the length and breadth?

And for the volume - it's simply the product of the length, breadth, and height, all of which you are given...
• Jun 24th 2009, 08:34 AM
masters
Quote:

Originally Posted by andyboy179
i need to know how to work out the volum and surface area of this shape, if you know how to please post:

Attachment 11980

Hi andyboy179,

This shape would appear to be a rectangular prism.

The lateral area (area of every side except top and bottom) is given by the formula:

LA = ph (perimeter of the base multiplied by the height)

The surface area is then found by adding the LA to the areas of the Bases (top and bottom).

SA = LA + 2B

LA = 18 times 3 = 54 square cm

SA = 54 + 2(14) = 82 square cm

The volume of a right rectangular prism is given by the formula:

V = LWH (length times width times height)

V = 7 X 2 X 3 = 42 cubic cm.
• Jun 24th 2009, 08:36 AM
andyboy179
Quote:

Originally Posted by Unenlightened
How much of this type of stuff have you done in school?
Could you get the area of a square, if you were given the length and breadth?

And for the volume - it's simply the product of the length, breadth, and height, all of which you are given...

hi thanks for posting, we havent done anything on it but she gave us one question on our homework, i think she said she will teach us it next lesson.
• Jun 24th 2009, 08:49 AM
andyboy179
im still confused, right could we do the volume first, how would i do that?
• Jun 24th 2009, 08:51 AM
e^(i*pi)
Quote:

Originally Posted by andyboy179
im still confused, right could we do the volume first, how would i do that?

As your shape is a cuboid you may multiply the width by the height by the depth. In this case it's multiplying the three numbers you are given together
• Jun 24th 2009, 08:52 AM
Unenlightened
Fair enough.
Well, on the offchance you can't understand masters' explanation; the easiest way to get the area is just to say: Total surface area = Sum of the areas of each face.
So you've six faces, all rectangles. The area of a rectangle is obtained by just multiplying the two sides.
So, say, the face at the top is 7x2 = 14.
And the face at the bottom will be the same = 14.
The face in front is 7x3=21
As is the one at the back = 21.
The other face you can see is 3x2 = 6.
And the corresponding one that you can't see =6 also.

So the sum of the four squares is 14+14+21+21+6+6 = 82.
• Jun 24th 2009, 08:55 AM
andyboy179
Quote:

Originally Posted by e^(i*pi)
As your shape is a cuboid you may multiply the width by the height by the depth. In this case it's multiplying the three numbers you are given together

would i do 7cm X 2cm=14cm
14cm X 3cm=52cm would 54cm be the volume?
• Jun 24th 2009, 08:58 AM
e^(i*pi)
Quote:

Originally Posted by andyboy179
would i do 7cm X 2cm=14cm
14cm X 3cm=52cm would 54cm be the volume?

You have the right method but your arithmetic is incorrect: 14 x 3 = 42 neither 52 nor 54.
• Jun 24th 2009, 08:58 AM
Unenlightened
Quote:

Originally Posted by andyboy179
would i do 7cm X 2cm=14cm
14cm X 3cm=52cm would 54cm be the volume?

14x3 =42, but yes, that's the right answer..

Edit: Gah! beaten to it (Thinking)
• Jun 24th 2009, 09:00 AM
andyboy179
sorry thats what i meant, silly me. now the surface area, i have no idea on how to do this could u help please?
• Jun 24th 2009, 09:13 AM
masters
Quote:

Originally Posted by andyboy179
sorry thats what i meant, silly me. now the surface area, i have no idea on how to do this

Whatever the rectangular prism is sitting on, we'll call that the base. In your case, the base is 7 by 2. The top is the same shape as the base, so it is also 7 by 2.

The Surface Area is found by adding the areas of all the faces or more simply, if the base is "l" by "w" and the height is "h", then the surface area is given by:

SA = 2(lw + hl + hw)

Another method I already gave you in my earlier post.
• Jun 24th 2009, 09:40 AM
HallsofIvy
The surface of the figure consists of 6 rectangles. The area of a rectangle is "height times width". Calculate the area of each rectangle and add them (opposite rectangles will have the same area so you really only need to find 3 areas).