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#1 2015-10-15 23:06:15

mathster
Member
Registered: 2015-10-09
Posts: 15

Quick problem.

Alana is making a ball out of rubber bands. When the ball has 54 rubber bands, it has a diameter of 3 cm. How many rubber bands should Alana add to the ball to increase its diameter by 1 cm? Assume that all of Alana's rubber bands have the same volume.

I am getting 74. Could anyone please tell me if that's correct? Thanks.

(with 54 rubber bands).

(with new amount of rubber bands).


Is my solution correct?

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#2 2015-10-15 23:40:12

David
Member
From: Bumpkinland
Registered: 2014-04-23
Posts: 3,164

Re: Quick problem.

Hi;

I could be wrong, wait for an expert.
[WRONG

David.

Last edited by David (2015-10-16 01:55:33)


His dominion is an everlasting dominion, Which shall not pass away, And His kingdom the one Which shall not be destroyed.

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#3 2015-10-16 01:17:07

Bob
Administrator
Registered: 2010-06-20
Posts: 10,053

Re: Quick problem.

hi mathster

I also get 74 bands by the same method.  smile

Bob


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 smile

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#4 2015-10-16 01:55:10

David
Member
From: Bumpkinland
Registered: 2014-04-23
Posts: 3,164

Re: Quick problem.

I might need some explanation.


His dominion is an everlasting dominion, Which shall not pass away, And His kingdom the one Which shall not be destroyed.

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#5 2015-10-16 03:30:02

Bob
Administrator
Registered: 2010-06-20
Posts: 10,053

Re: Quick problem.

hi David

The diameter at first is 3cm so the radius is 3/2 cm.  So you can work out the volume and divide by 54 to get the volume of a single band.

Now compute the increase in volume (with a new radius of 2):

Now divide this by the volume of a band to get how many more you will need:

Hope that helps,

Bob

ps.  I didn't look at how you got your answer.  Maybe it was mostly right.  smile  If you re-post it I'll see if I can see what went wrong.  Don't worry about posting something that may be wrong.  It happens to me a lot.  eek shame


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 smile

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#6 2015-10-16 09:06:26

David
Member
From: Bumpkinland
Registered: 2014-04-23
Posts: 3,164

Re: Quick problem.

I see what is wrong now... I squared the radius... LOL! Thanks!


His dominion is an everlasting dominion, Which shall not pass away, And His kingdom the one Which shall not be destroyed.

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