Maths questions ? answers and method needed ! ( help)

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Katchi_2003
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1. The diameter of cylindrical marble column is 60 cm and its height is 4.2M. The cost of making this column is quoted as £67.50 a cubic metre. What is the estimated total cost of making this column ?

answer should be £80.

2. Find the weight of a solid iron cylinder 55cm high with a base diameter of 60cm. The density of 60cm. The density of iron is 7.9g/Cm3.

Answer should be 1228 kg

3. What is the radius of a cylinder 7 cm long and with a volume of 200cm3.

Answer should be 3.99cm

i need methods plse i am really stuck with these 3 questions, thank you very much i would be grateful.
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theone
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(Original post by Katchi_2003)
1. The diameter of cylindrical marble column is 60 cm and its height is 4.2M. The cost of making this column is quoted as £67.50 a cubic metre. What is the estimated total cost of making this column ?

answer should be £80.

2. Find the weight of a solid iron cylinder 55cm high with a base diameter of 60cm. The density of 60cm. The density of iron is 7.9g/Cm3.

Answer should be 1228 kg

3. What is the radius of a cylinder 7 cm long and with a volume of 200cm3.

Answer should be 3.99cm

i need methods plse i am really stuck with these 3 questions, thank you very much i would be grateful.
1. Volume = pi.r^2.h = 4.2 x 0.09 . pi = 1.187m^3 so the cost is 1.187 . 67.50 = 80.16 pounds.

2. Volume = 55 x 900 x pi = 155509 cm^3 If the density is 7.9g/cm^3 the mass is .0079kg x 155509cm^3 = 1228.52 Kg

3. V = pi.r^2.h So 200 = pi.r^2.7 So r^2 = 9.0946 So r = 3.01 cm
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Katchi_2003
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(Original post by theone)
1. Volume = pi.r^2.h = 4.2 x 0.09 . pi = 1.187m^3 so the cost is 1.187 . 67.50 = 80.16 pounds.

2. Volume = 55 x 900 x pi = 155509 cm^3 If the density is 7.9g/cm^3 the mass is .0079kg x 155509cm^3 = 1228.52 Kg

3. V = pi.r^2.h So 200 = pi.r^2.7 So r^2 = 9.0946 So r = 3.01 cm
For question 1 how did you get 0.09, and question 2 how you got 900 ??,
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PQ
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(Original post by Katchi_2003)
For question 1 how did you get 0.09, and question 2 how you got 900 ??,
r^2=60cm/2 ^2=0.3m^2=0.09

again

r^2=(60/2)^2=30^2=900
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Katchi_2003
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(Original post by Pencil Queen)
r^2=60cm/2 ^2=0.3m^2=0.09

again

r^2=(60/2)^2=30^2=900
Thanks alot, i was also referrring to question 2 how did the guy get 900 ?
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Katchi_2003
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3. V = pi.r^2.h So 200 = pi.r^2.7 So r^2 = 9.0946 So r = 3.01 cm ?

how you got 2.7 ?

I hate when i cant figure how i got it, its taking ages for me to find how to do that method regarding 2.7 ? please someone give me a detailed explaination.
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PQ
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(Original post by Katchi_2003)
Thanks alot, i was also referrring to question 2 how did the guy get 900 ?
r^2=(60/2)^2=30^2=900

how you got 2.7
It's not 2.7 it's r^2 * 7 (if you look before the 7 is inserted it's shown as r^2.h) - the dot means multiplied
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louby
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(Original post by Katchi_2003)
1. The diameter of cylindrical marble column is 60 cm and its height is 4.2M. The cost of making this column is quoted as £67.50 a cubic metre. What is the estimated total cost of making this column ?

answer should be £80.

2. Find the weight of a solid iron cylinder 55cm high with a base diameter of 60cm. The density of 60cm. The density of iron is 7.9g/Cm3.

Answer should be 1228 kg

3. What is the radius of a cylinder 7 cm long and with a volume of 200cm3.

Answer should be 3.99cm

i need methods plse i am really stuck with these 3 questions, thank you very much i would be grateful.
plz can u help me solve equtions cos i dont under stand them
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meepmeep
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(Original post by louby)
plz can u help me solve equtions cos i dont under stand them
Any particular type of equation or just "equations"? Otherwise it's a little vague... :confused:
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Katchi_2003
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(Original post by Pencil Queen)
r^2=(60/2)^2=30^2=900



It's not 2.7 it's r^2 * 7 (if you look before the 7 is inserted it's shown as r^2.h) - the dot means multiplied
i am a pain i know but how do you find r to do pi.r^2 lol
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PQ
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(Original post by Katchi_2003)
i am a pain i know but how do you find r to do pi.r^2 lol
r is what you are trying to find...look again at the answer you were first given

V = pi * r^2 * h

add in the numbers you are given

200 = pi * r^2 * 7

move all the numbers over to one side leaving just r^2 on the other side

200/(pi * 7) = r^2

200/22.0 = r^2

9.0946 = r^2

squareroot of 9.0946

r = 3.01 cm
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Katchi_2003
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(Original post by Pencil Queen)
r is what you are trying to find...look again at the answer you were first given

V = pi * r^2 * h

add in the numbers you are given

200 = pi * r^2 * 7

move all the numbers over to one side leaving just r^2 on the other side

200/(pi * 7) = r^2

200/22.0 = r^2

9.0946 = r^2

squareroot of 9.0946

r = 3.01 cm
You are a queen thank you very much for your help, more Pencil queens will make the world so much easier ! cheers BTW.
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