Pre Algebra help? Given 10 pts

These were the only questions I got stuck on, thanks in advance!!!!! :D



1. What is the approximate circumference of a semicircle with a radius of 12 centimeters?
(Points : 1)
18.8 centimeters

37.7 centimeters

75.4 centimeters

150.7 centimeters


2 and 3.

http://img132.imageshack.us/img132/1411/110609204816.png


4. 4. A pizza has a diameter of 16 inches. What is the approximate circumference of the pizza?
(Points : 1)
100.5 inches

50.2 inches

25.1 inches

12.6 inches


5. 5. A wheel has a radius of 15 cm. Approximately how far does it travel in 4 revolutions?
(Points : 1)
47.1 cm

94.2 cm

188.4 cm

376.8 cm

1. The circumference is 12pi so your answer is 37.7
2. 21.4
3. 7.1
4. 16pi or 50.2
5. 376.8

All of these involve the formula for circumference of a circle, which is C = 2π r
1. It's a semicircle, so you only need πr = 3.14 *12 = 37.7 cm

2. Calculate the circumference of the semicircle part first 3.14*6 = 18.84
Add that to the other 3 sides: 6 + 3 +3 + 18.84 = 30.8 mm

3. radius is 2; you want the circumference of 1/4 of a circle, so π r/2 = 3.14
Add that to the other sides 3.14 + 2 +2 = 7.1

4. This time you're given the diameter instead of the radius, so the formula becomes π d
3.14 * 16 = 50.2 inches

5. Circumference 2 π * 15 = 94.2 cm
In four revolutions it travels 4*94.2 = 376.8

I hope that helps you to understand these, so that you won't get stuck on similar problems.