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by romitvsingh » Fri Mar 23, 2012 11:09 pm
The curved surface of a cylinder is 264m^2.Its volume is 924m^3. The height of the cylinder must be

a 4m

b 6m

c 8m

d none of these
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by killer1387 » Fri Mar 23, 2012 11:21 pm
romitvsingh wrote:The curved surface of a cylinder is 264m^2.Its volume is 924m^3. The height of the cylinder must be

a 4m

b 6m

c 8m

d none of these
b 6M
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by rijul007 » Sat Mar 24, 2012 12:00 am
Curved Surface area = 2Ï€rh = 264
Ï€rh =132 = 4*3*11

Volume = πr²h = 924 = 4*3*7*11

Ï€rh*r = 924
r = 7

Ï€rh = 132
3.14*7*h = 132
22h ≈ 132
h ≈ 132/22
h ≈ 6

IMO B
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by Brent@GMATPrepNow » Sun Mar 25, 2012 6:13 am
romitvsingh wrote:The area of curved surface of a cylinder is 264m^2.Its volume is 924m^3. The height of the cylinder must be
a 4m
b 6m
c 8m
d none of these
The area of the curved surface of a cylinder = 2(pi)rh
So, if this area is 264, we can write 2(pi)rh = 264
Divide both sides by 2 to get (pi)rh = 132

The volume of a cylinder = (pi)(r^2)h
So, if the volume is 924, we can write (pi)(r^2)h = 924

From here, we can "divide" the equations to get:
(pi)(r^2)h/(pi)rh = 924/132
Simplify to get: r=7

Now that we know the value of r, we can plug this value into either equation to find the value of h.

How about: (pi)(7)h = 132
This means that h = 132/7pi
As you can see, h cannot be an integer, so the answer must be D.

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Brent
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by romitvsingh » Tue Mar 27, 2012 10:59 am
Brent@GMATPrepNow wrote:
romitvsingh wrote:The area of curved surface of a cylinder is 264m^2.Its volume is 924m^3. The height of the cylinder must be
a 4m
b 6m
c 8m
d none of these
The area of the curved surface of a cylinder = 2(pi)rh
So, if this area is 264, we can write 2(pi)rh = 264
Divide both sides by 2 to get (pi)rh = 132

The volume of a cylinder = (pi)(r^2)h
So, if the volume is 924, we can write (pi)(r^2)h = 924

From here, we can "divide" the equations to get:
(pi)(r^2)h/(pi)rh = 924/132
Simplify to get: r=7

Now that we know the value of r, we can plug this value into either equation to find the value of h.

How about: (pi)(7)h = 132
This means that h = 132/7pi
As you can see, h cannot be an integer, so the answer must be D.

Cheers,
Brent
your ans is wrong its b) 6
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by Brent@GMATPrepNow » Tue Mar 27, 2012 11:18 am
romitvsingh wrote: your ans is wrong its b) 6
The height of the cylinder is 132/(7pi). This does not equal 6.
Sure, it's close to 6 (6.002414997etc), but it does not equal 6.

On the GMAT, the wording in the original question would never allow for 132/(7pi) to equal 6.

If we were to rewrite the original question to fit GMAT's sense of mathematical correctness, it would look something like this:

The area of the curved surface of a cylinder is 264, and its volume is 924. Which of the following is the best approximation of its height?
A) 4
B) 6
C) 8
D) 10
E) 12

Here, the word "approximation" allows for some wiggle room regarding the accuracy of the solution, the removal of the answer choice "none of these" eliminates ambiguity, and 5 answer choices (instead of 4) fits the GMAT standard.

Cheers,
Brent
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by ronnie1985 » Wed Mar 28, 2012 10:36 am
simple calculations yield the result of 12 m
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