Math Is Fun Forum

Arna

Member

From: The Polar Plane

Registered: 2014-07-23

Posts: 1,668

An equal problem

The ratio between the curved surface area and the total surface area of a right circular cylinder is 1:2 . Find the ratio between the height and radius of the cylinder

A part of the solution reads:
2h=h+r
>h=r
>h:r=1:1

My question is why should it be 1:1?
For example if x and y and z are 3 numbers
and x=y
x=z
>y=z>y:z
Substituting x, y, and z
2=4
2=3
>4=3>4:3
Then why only 1:1??

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Nothing is impossible as the statement itself states I M POSSIBLE
In this realm of twisted reality,sanity is only illusion

Agnishom

Real Member

From: Riemann Sphere

Registered: 2011-01-29

Posts: 25,002

Website

Re: An equal problem

I do not get any of what you wrote.

Why is 2=4?

Last edited by Agnishom (2014-10-22 19:41:10)

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'And fun? If maths is fun, then getting a tooth extraction is fun. A viral infection is fun. Rabies shots are fun.'
'God exists because Mathematics is consistent, and the devil exists because we cannot prove it'
I'm not crazy, my mother had me tested.

Bob

Administrator

Registered: 2010-06-20

Posts: 10,636

Re: An equal problem

hi Arna

I also am confused by what you have written.  Maybe you are using the wrong symbols?

=  equal

Two numbers are equal if they are the same.

eg.

: is used to show a ratio.

eg.  If there are three times as many children in a room as adults then    children : adults = 3 : 1

>y=z>y:z

This line is incomplete.  You have said that y equals z implies the ratio of y to z is ?????

x=y
x=z

Substituting x, y, and z
2=4
2=3

If the numbers are equal then you cannot have different numbers for x y and z.

I'll go back to the original problem.

curved area : total area = 1:2

implies curved area : curved area + top and bottom = 1 : 2

implies curved area : top and bottom = 1 : 1

This means they are equal so

Bob

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Children are not defined by school ...........The Fonz
You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei
Sometimes I deliberately make mistakes, just to test you!  …………….Bob

Arna

Member

From: The Polar Plane

Registered: 2014-07-23

Posts: 1,668

Re: An equal problem

Thank you Bob for clearing my confusion

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Nothing is impossible as the statement itself states I M POSSIBLE
In this realm of twisted reality,sanity is only illusion

Olinguito

Member

Registered: 2014-08-12

Posts: 649

Re: An equal problem

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Bassaricyon neblina

Arna

Member

From: The Polar Plane

Registered: 2014-07-23

Posts: 1,668

Re: An equal problem

Thank you Oliinguito

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Nothing is impossible as the statement itself states I M POSSIBLE
In this realm of twisted reality,sanity is only illusion