my blog post

okay class, we were all assigned questions, and i got question 7 from section 1.3 in our textbooks.



For the first part of question 7 it asks for the dimensions of the cut out piece. If you look at the image above the cut out piece is in the corner.

So to find the dimensions you could see that they are:
9cm, 15cm, and 17cm.

Then for part two, it asks how the cut out piece will affect the surface area for the original rectangular solid. But truth is it doesn't.

It shows the top, side, and front view of the solid, but it shows a whole surface! So the surface area stays the same because cutting out a CORNER piece will only affect the volume. But if you look at the piece at front, side, and top view. The shape looks perfectly normal!

What we learned:
The dimensions of the cut out piece is 9cm, 15cm, and 17cm

Sometimes cutting out a corner on a prism will not affect the surface area

Mary Jane's Scribepost for October 5, 2010

In today's math class, we were all assigned to do a blogpost on surface area. For my blog I was assigned to do question 1 (chapter 1.3) in the homework book.



Key Ideas Review:



1. Complete the chart below, using the first row as a sample. Show your answer to the nearest tenth.

*NOTE: The surface area for the triangle was supposed to be 1.5m (squared)

Calculations:


Square: A = l x w

= 10 x 10

= 100 cm (squared)




Rectangle: A = l x w

= 30 x 22.5

= 675 cm (squared)




Circle: A = pi x r squared

= pi x (15 x 15)

= pi x 225

= 706.9 cm (squared)



Rectangular Prism: A = 2(lw) + 2(lh) + 2(hw)
= 2(25 x 12) + 2( 25 x 12) + 2( 12 x 12)
= 2(300) + 2(300) + 2(144)
= 600 + 600 + 288
= 1488 cm (squared)


Cylinder: A = 2 [(pi)(r) squared] + 2 (pi)[( r x h)]

= 2 [(pi) (4 x 4)] + 2[ (pi) (4 x 15)]

= 2 (pi) (16) + 2 (pi) (60)

= 2 (50.3) + 2 (188.5)

= 100.6 + 377

= 477.6 cm (squared)

* NOTE: I rounded the answer for pi x 16 and pi x 60 to the nearest tenth which is why my answer is 0.1 higher.




Triangle: A = 1/2 b x h


= 1 x 1.5


= 1.5 cm (squared)

My Examples:

Square: One side of a box: 20 cm by 20 cm

A = l x w

= 20 x 20

= 400 cm (squared)

Rectangle: A wooden door: 35 cm by 23

A = l x w

= 35 x 23

= 805 cm (squared)

Circle: One side of a car tire: Radius of 17 cm

A = pi x r squared

= pi x (17 x 17)

= pi x 289

= 907.9 cm (squared) nearest tenth

Rectangular Prism: Math textbook: l= 7 cm w= 8 cm h= 5 cm

A = 2(lw) + 2(lh) + 2(hw)

= 2( 7 x 8) + 2(7 x 5) + 2(5 x 8)

= 2 (56) + 2(35) + 2(40)

= 112 + 70 + 80

= 262 cm (squared)

Cylinder: Hairspray Can: 13 cm high and 6 cm for radius

A = 2 [pi r (squared)] + 2 [pi (r x h)]

= 2 [pi (6 x 6)] + 2 [pi (6 x 13)]

= 2 (pi x 36) + 2 (pi x 78)

= 2 x 113.1 + 2 x 245

= 226.2 + 490

= 716.2 cm (squared)

*NOTE I rounded the answer for pi x 36 and pi x 78 to the nearest tenth.

Triangle: End of a Toblerone Package: 4 cm for base and 2.5 cm high

A = 1/2 b x h

= 2 x 2.5

= 5cm (squared)

Thank you for reading my blog and please don't forget to COMMENT !

Jomari's Post October 5, 2010

5.Silvio wants to cover the stairs of his basement, There are 14 treads, or steps, and 14 risers. Each step is 90 cm wide and 24 cm deep. Each riser is 90 cm and 18 cm high. The diagram shows some of the stairs

A. What is the surface area of the step treads?
24cmx90cm = 2160cm²
2160cm² = one step tread
2160cm² x 14 = 30240cm²
Surface Area of all treads = 30240cm²
B. What is the surface area of the risers ?
18cm x 90 cm = 1620cm²
1620cm² = one riser
1620² cm x 14 = 22680cm²
Surface Area of all risers = 22680cm²
C.What is the total surface area of the part of the stairs that Silvio wants to cover?
22680cm² + 30240cm² = 52920cm²

Binesi's Blog Post

Today in class I was assigned question 9 to do for the blog.

Examine the bookshelf. It is constructed of thin hardwood. The top, bottom, and all three shelves are the same size. There is an equal distance between the top, the shelves, and the base.

a) What is the surface area of one shelf?

A= l x w (2)

A= 90 x 24 (2)

A= 4 320 cm

You have to multiply by two because theres both a top and bottom in the smaller inside shelf.

b) What is the total surface area of the bookcase?

For the tops and undersides of the entire bookshelf you have to go Length x Width x 10

I got the 10 because there are 5 identical surfaces (add both sides of them equals 10)

The sides of shelves (There are 2 but you have to do both sides)

120 x 24 x 4 = 11 520cm

The very back of the shelf (Multiplied by 2 both sides)

90 x 120 x 2 = 21 600

You add all of the pieces together :

TSA= 21 600+11 520+21 600

TSA= 54 720cm

c) What is the fewest number of surfaces for which you need to find the surface area in order to answer part b?

Only 3 (the back, the small inner shelf and the side shelf)