Wednesday, January 26, 2011

Questions 15 and 16

Question 15:

a) If the edge length of a cube is doubled, find the ratio of the old surface area to the new surface area.
b) What happens if the edge length of a cube is tripled? Is there a pattern?

a) 1:4. Instead of thinking of it as a cube, I thought of it as a square. Let's say a side of a cube's side lengths were 6m and had an area of 36cm2. You multiply the side lengths by 2, which becomes 12, and find the new area which is 144. 144/36=4. So, the ratio is 1:4.

b) If the side length is tripled, the new ratio becomes 1:9. There is a pattern if you continue doing this. All of the lengths are prime numbers while the other numbers stay the same. For example, 1:4, 1:9, 1:16, 1:25. ( x 4=64)

Question 16:

Shelby wants to paint the walls and ceiling of a rectangular room. 1 liter of paint covers 9.5 m2.

a) What is the least amount of paint Shelby can buy to paint the room (subtract 5 m2

for the door and windows)?
b) How much will the paint cost, including the amount of tax charged in your region?

The height is 2.6m2, the length is 4.8m2, the width is 6.8m2. 1 liter of paint covers 9.5 m2.

a) L x W
2.6 x 4.8
2.6 x 4.8
2.6 x 6.8
2.6 x 6.8
6.8 x 4.8
6.8 x 4.8=
125.6 125.6-5= 120.6
120.6-65.28 (the ceiling paint has to be separated from the wall paint)= 55.32

Wall paint: 1 can 4L, 2 cans 1L.
Ceiling paint: 1 can 4L.

b) The cost will be 82.75 with 12% GST and PST.

Wall paint: 4L= $24.95
Ceiling paint: 4L=$32.95

12%= 8.87.
73.88+8.87= 87.75

Here is a video to help you with surface area:
Here is a website to help you:

Cylinder Volume and Volume Problems

a) (π x r x r) x h
(3.14 x 5 x 5)x 8
78.5 cm2 x 8cm

b) (π x r x r) x h
(3.14 x 11 x 11) x 11
379.94 x 11

c)(π x r x r) x h
(3.14 x 1.1 x 1.1) x 2.6
3.7994 x 2.6

d) (π x r x r) x h
(3.14 x 4.5 x 4.5) x 25
56.52 x 25

with inside diameter:
(π x r x r) x h
(3.14 x 4 x 4) x 40
50.24 x 40

with outside diameter:
(π x r x r) x h
(3.14 x 5 x 5) x 40
78.5 x 40

3140-2009.6= 1130.4

capacity of pipe 1130.4cm3


  1. Excellent job Suzie! You did an great job at explaining everything and add understandable pictures to accompany/support your text very well, but one thing that I would suggest is that only use color for the titles, questions, or important information only. Other than that it was a great post!

  2. Wow, great job Suzie. You explained things pretty well. I think you need work on easing up on the color, it's a bit distracting, and the fonts sizes are not always consistent.

  3. Great job Suzie, You explained your answer really well. I also liked that your post is very organized. Next time you should just embed the video, add the link on a word and less color.

  4. Great job Suzie. Your post is very colorful and it is really organized and neat. I agree with Paul that you should embed the video and make it into a word. Other than that, great job.

  5. Good job Suzie! Your post is very sexylicious and colour two things I love! Though it may be a bit distracting and half the font is bigger.