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Vakman

November 10th, 2009, 11:18 PM

A city park contains a cylindrical artificial pond that has a radius of 7.5M. A 2M concrete deck will be constructed around the pond. the concrete should be at least 15CM thick. Calculate the minimum volume of concrete required to construct the deck.

Thanks.

No answer sheet, so I think I was right, but if anyone knows?

Would help a friend of mine out. Have not taken math in a couple years xD

kyuubi777

November 10th, 2009, 11:21 PM

you just calculate the volume of the large cylinder and subtract the volume of the small

the eqtn for volume of a cylinder is (h pi r^2) = volume

koleoptero

November 10th, 2009, 11:25 PM

1.884 cubic meters

EDIT: No wrong.

EDIT 2: 16.022122535 m^3

Chronon

November 10th, 2009, 11:29 PM

1.884 cubic meters

The answer should have only one significant figure, so 2 cubic meters. If the 2 m dimension is exactly specified then the answer would have 2 significant figures (digits) so V = 1.9 m^3.

EDIT: okay then either 20 cubic meters or 16 cubic meters depending on the number of significant digits the answer should have.

Barrucadu

November 10th, 2009, 11:31 PM

r = 9.5

R = 7.5

h = 0.15

v = πh(r^2 - R^2)

= 0.15π × 34

= 5.1π

There.

koleoptero

November 11th, 2009, 12:57 AM

The answer should have only one significant figure, so 2 cubic meters. If the 2 m dimension is exactly specified then the answer would have 2 significant figures (digits) so V = 1.9 m^3.

EDIT: okay then either 20 cubic meters or 16 cubic meters depending on the number of significant digits the answer should have.

I'm a mathematician, all digits are important to me. ;) :P

NoaHall

November 11th, 2009, 01:01 AM

I'm a mathematician, all digits are important to me. ;) :P

I'm a mathmagican, eat my pii.

kyuubi777

November 11th, 2009, 01:29 AM

answers 44 it's real easy cause the sig figs .. you got 45 u roundn high ur answers too big..

http://www.youtube.com/watch?v=Ooa8nHKPZ5k

saulgoode

November 11th, 2009, 02:22 AM

r = 9.5

R = 7.5

h = 0.15

v = πh(r^2 - R^2)

= 0.15π × 34

= 5.1π

There.

You left out pi.

EDIT: my mistake. The symbol did not appear in my browser.

Chronon

November 11th, 2009, 02:42 AM

I'm a mathematician, all digits are important to me. ;) :P

Fair enough.

Vakman

November 12th, 2009, 01:06 AM

Okay, thanks xD

I was just checking for a friend.

Thanks all.

afeasfaerw23231233

November 12th, 2009, 08:32 AM

I think this should be the answer:

http://www.codecogs.com/eq.latex?2\pi(7.65^2-7.5^2)=14.28

14.28 m^3 (4 s.f.)

1.884 cubic meters

EDIT: No wrong.

EDIT 2: 16.022122535 m^3

Would you please tell us how did you get that number?

r = 9.5

R = 7.5

h = 0.15

v = πh(r^2 - R^2)

= 0.15π × 34

= 5.1π

There.

Aren't

r = 7.65

h = 2

?

Considering a pond that has a radius of 7.5M, it would be quite ridiculous to have a deck which has a width of 2m and a height of 0.15m!

bonfire89

November 12th, 2009, 08:41 AM

If you wanted to make this way more complicated then need be you could solve it with calculus http://tutorial.math.lamar.edu/Classes/CalcI/VolumeWithRings.aspx :P

Barrucadu

November 12th, 2009, 09:00 AM

Considering a pond that has a radius of 7.5M, it would be quite ridiculous to have a deck which has a width of 2m and a height of 0.15m!

Well, that's what the question says. A desk of 2m with a height of 15cm.

afeasfaerw23231233

November 12th, 2009, 09:02 AM

But who would need calculus to do such a simple job? haha :)

If OP has any problem of math I recommend http://www.mathhelpforum.com .

afeasfaerw23231233

November 12th, 2009, 09:05 AM

Well, that's what the question says. A desk of 2m with a height of 15cm.

Isn't 15cm referring to the thickness? If 15cm is the height then I am wrong and you are right.

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