## Tuesday, October 5, 2010

### 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 !