Tuesday, October 5, 2010

Brayden's Blog Post

For homework today everyone had to make a blog on 1 question. The question I recieved was..

A rectangular prism measures 16cm by 8cm by 5cm. It is cut so that the 16cm side is cut in half. How does the surface area of the half prism compare to the surface area of the original prism?

First I had to find the surface area of the original prism.

L = 16cm W = 8cm H = 5cm

S.A. = 2 (l x w) + 2 (l x h) + 2 (w x h)
S.A. = 2 (16 x 8) + 2 (16 x 5) + 2 (8 x 5)
S.A. = 2 (128) + 2 (80) + 2 (40)
S.A. = 256cm + 160cm +80cm
S.A. = 496cm2

Then I had to find the surface area of the half prism.

L = 8cm W = 8cm H = 5cm

S.A. = 2 (l x w) + 2 (l x h) + 2 (w x h)
S.A. = 2 (8 x 8) + 2 (8 x 5) + 2 (8 x 5)
S.A. = 2 (64) + 2 (40) + 2 (40)
S.A. = 128cm + 80cm + 80cm
S.A. = 288cm2

Now to compare.

You would think that cutting the prism would mean that the surface area is divided by 2, but, it isn't. It is not half because when you split it vertically the only dimension that changes is the length. So when you are multiplying width by height it will be the same as the original prism. When you look at the answer every thing is cut in half except the width by height. Therefore the surface area of the half prism is not half the surface area of the original prism.

Please correct me on my mistakes.

COMMENT!

1. that's nice.

2. This comment has been removed by the author.

3. Good Job Brayden!!

4. I like your explanation, it makes sense.

5. Good job Brayden. It was very well explained.

6. Nice post Brayden but I think you should have made an image or some sort of picture so we know what the shape looks like. Overall I think you did a great job and showed the formula and everything, and I like the last part (compare) which showed how you compared it Great job !.