Asked by Sebby-Chan

I was wondering if you can help me with math real quickly. I just cant figure this out.

For the first question I have to find the surface area for the given cylinder. I have to use 3.14 and round to the nearest whole number. The radius is 6ft and the height is 20 ft.

A. 180 ft2
B. 720 ft2
C. 433 ft2
D. 135 ft2

For the second question I have to find the lateral area for the given cylinder. I have to use 3.14 and round to the nearest whole number. The radius is 6 yd, and the height is 24 yds.

A. 144 yd2
B. 288 yd2
C. 2,712 yd2
D. 904 yd2

No matter how much I work on the problems I still cant get the right answer. Can you please help? Thanks.
Answered by Reiny
Imagine "opening up" a cylinder, what would you get?

2 equal circles + a rectangle whose length is the circumference of the circle and whose height is the height of the cylinder.

so SA = 2π(6^2) + 2π(6)(20)
= 72π + 240π = 312π = appr 980
No wonder you can't figure it out, none of the answers are correct


for the 2nd:
SA = 2π(6^2) + 2π(6)(24)
= 72π + 288π = 360π = appr 1131

Are these the answers you got?
Answered by Steve
a = 2pi*r(r+h) = 2pi*6*26 = 979.68
Hmmm. That includes both ends. The lateral area is
a = 2pi*r*h = 2pi*6*20 = 753.6
Is there a typo somewhere?

2pi*6*24 = 904.3, so (D)
Answered by Sebby-Chan
@Reniy: Yes those were the answers I came up with. I couldn't figure out what I was doing wrong, turns out I was doing the first one right and the second one was a bit off. Thank you for the help.
Answered by Sebby-Chan
@Steve: Thank you for the help as well, no there isn't a typo. Sometimes the math we're doing is quite confusing. Thank you for the help. c:
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