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2 Geometry ques...stuck

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2 Geometry ques...stuck  [#permalink]

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New post 24 Feb 2008, 04:19
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E

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Hi everyone,

I came across a ques in solid geometry and I was stuck.

Q- A 5 foot long cylindrical pipe has an inner diameter of 6 feet and an outer diameter of 8 feet. If the total surface area (inside and out, including the ends) is k*pie, what is the value of k ? :?:

(a) 7 (b) 40 (c) 48 (d) 70 (e) 84

(Pie = 22/7)

Can anyone solve it with an explanation. Moreover whats the diff between curved surface area and total surface area ?

Q-2 In the figure (below) all of the following are equal Except - :!:

(a) ab (b) ac (c) ad (d) bc (e) bd

The above ques is coordinate geometry ques. i didnt get it. can anyone solve it as well. (Figure attached)

Thanks a lot, :)
GR
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Re: 2 Geometry ques...stuck  [#permalink]

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New post 24 Feb 2008, 08:07
1st is E.
couldnt understand the 2nd :(
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Re: 2 Geometry ques...stuck  [#permalink]

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New post 24 Feb 2008, 08:35
vscid wrote:
1st is E.
couldnt understand the 2nd :(


Well I also know the answer is E. All I need is an explanation.
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Re: 2 Geometry ques...stuck  [#permalink]

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New post 24 Feb 2008, 09:40
1
Ist question :

Since it is a solid pipe so total surface area is different from curved surface area as in this case total surface area will be curved surface area both inside and outside of the pipe plus surface area of ends of pipe.

Total surface area = 2X ( surface area of each end as there are two similar ends ) + curved
surface area outside + curved surface area inside

surface area of each end= pi ( R^2- r^2) = pi (16-9)
curved surface area outside of pipe= 2 X pi X 4 X 5= 40pi
curved surface area inside of pipe = 2X pi X 3 X 5= 30pi
Total sufrace area= 14pi +70pi = 84pi
k=84

ii question

From given quardinates
b=0
c=0

therefore
ab=0
ac=0
bc=0
only non zero is ad
so ad is the answer

I hope explanation is clear
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Re: 2 Geometry ques...stuck  [#permalink]

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New post 24 Feb 2008, 09:47
greatchap wrote:
vscid wrote:
1st is E.
couldnt understand the 2nd :(


Well I also know the answer is E. All I need is an explanation.

sure dude.
here it is:
area of the internal as well as external surface of the cylinder is 2*pi*r*h, which gives 30pi and 40pi respectively.
total area of the two ends = 2[pi* (r1^2 - r2^2)]
which gives 2[pi * (16-9)]
= 14*pi
total area = 30pi+40pi+14pi
=84pi

E.

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Re: 2 Geometry ques...stuck  [#permalink]

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New post 24 Feb 2008, 10:42
Hi guys,

thanks a lot for your help and explanation. :)

I got a hang of the question. The only thing that I am confused :? about is -

surface area of each end= pi ( R^2- r^2) = pi (16-9)
OR
total area of the two ends = 2[pi* (r1^2 - r2^2)]

(both are same)

Ya, so how do we determine total surface area of two ends. when are we suppose to use that. And how did you get the formula 2*pi*(R^2 - r^2)

Cheers,
GR
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Re: 2 Geometry ques...stuck  [#permalink]

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New post 24 Feb 2008, 11:48
greatchap wrote:
Hi guys,

thanks a lot for your help and explanation. :)

I got a hang of the question. The only thing that I am confused :? about is -

surface area of each end= pi ( R^2- r^2) = pi (16-9)
OR
total area of the two ends = 2[pi* (r1^2 - r2^2)]

(both are same)

Ya, so how do we determine total surface area of two ends. when are we suppose to use that. And how did you get the formula 2*pi*(R^2 - r^2)

Cheers,
GR

since its a pipe, area is the difference between the outer area and the inner area.
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Re: 2 Geometry ques...stuck  [#permalink]

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New post 21 May 2014, 11:02
2
First Question.

Height of Cylinder = 5 feet

Radius of inner circle = 6/2 = 3 feet

Radius of outer circle = 8/2 = 4 feet

Area of different parts are calculated as shown in figure..
Attachment:
File comment: Surface Area of Cylinder
gmatcylinder.jpg
gmatcylinder.jpg [ 44.82 KiB | Viewed 2588 times ]


Hence Answer is E
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Re: 2 Geometry ques...stuck  [#permalink]

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New post 26 Jun 2018, 03:47
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Re: 2 Geometry ques...stuck &nbs [#permalink] 26 Jun 2018, 03:47
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