## Thursday, February 3, 2011

### Ysabelle's Surface Area Scribe

Pages 186-187

7. Do you prefer to find the surface area of a cylinder by using the sum of the area of each face or by using a formula? Give at least two reasons for your choice.

A: I prefer to use a formula because it is quicker and I'm less likely to miss a part of the calculation.

9. Kaitlyn and Hakim each bought a tube of candy. Both containers cost the same amount . Which container required more plastic to make?

Container A:
diameter- 7 cm
height- 122 cm

SA=2.π.r.r+2.π.r.h
SA=2(3.14)(3.5)(3.5)+2(3.14)(3.5)(122)
SA=76.93+2681.56
SA=2758.49 cm²

Container B:
diameter- 11 cm
height- 85 cm

SA=2.π.r.r+2.π.r.h
SA=2(3.14)(5.5)(5.5)+2(3.14)(5.5)(85)
SA=189.97+2935.90
SA=3125.87 cm²

Container B required more plastic to make.

10. Paper towel is rolled around a cardboard tube. Calculate the outside surface area of the tube.

height- 27.5 cm

outside SA=2.π.r.h
outside SA=2(3.14)(2)(27.5)
outside SA=345.4 cm²

Cylinder Volume and Volume Problems

Solution:

JUMBO
r= d/2 r=20/2 r=10 cm V= πrrh V= [(3.14)(10)(10)](40) V= (314cm²)(40cm) V= 12560cm³

POPCORN LOVER'S
r=d/2 r=30/2 r=15 cm V= πrrh V= [(3.14)(15)(15)](20) V= (706.5cm²)(20cm) V= 14130cm³

Martha should buy Popcorn's Lover if she wants more popcorn for her money.

Solution:
outside
r=d/2
r=1/2

r=0.5m

V=πrrh

V=[(3.14)(0.5)(o.5)](10)
V=(o.785m²)(10m)
V=7.85m³

inside
r=d/2
r=0.8/2
r=0.4m

V=πrrh
V=[(3.14)(0.4)(0.4)](10)
V=(o.5024m²)(10m)
V=5.024m³

7.85m³-5.024m³=2.862m³ or 2.9m³

The volume of the concrete required to make the culvert is 2.9m³.