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PostPosted: Wed Apr 03, 2013 2:18 pm 
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I am stuck with this question. its from a 11+ sample paper of an independent school.

When freezing, water increases its volume by 1/11. By what part of its volume will
ice decrease when it melts and turns back into water?

Thanks


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PostPosted: Wed Apr 03, 2013 2:24 pm 
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henna025 wrote:
I am stuck with this question. its from a 11+ sample paper of an independent school.

When freezing, water increases its volume by 1/11. By what part of its volume will
ice decrease when it melts and turns back into water?

Thanks



could try with some figures -eg if you have 99 cm3 of water and freeze it it will be 99+9 = 108.

if you melt it it will be 9/108 smaller so 1/12 ?

works for others too... 44 cc - freeze becomes 44+4 = 48 melting gives 4/48 - so 1/12

am sure it can be done algebraically but brain not working today :lol:


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PostPosted: Wed Apr 03, 2013 3:05 pm 
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Removed because my post was more confusing than previously quoted..


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PostPosted: Wed Apr 03, 2013 4:08 pm 
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henna025 wrote:
When freezing, water increases its volume by 1/11. By what part of its volume will
ice decrease when it melts and turns back into water?

This means that the volume after freezing is 12/11 what it was when it was liquid.

Thus the volume after melting will be 11/12 what it was when it was frozen, a decrease of 1/12.


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PostPosted: Wed Apr 03, 2013 4:44 pm 
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Beyond me.


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PostPosted: Wed Apr 03, 2013 4:56 pm 
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Well put WP, exactly what I tried to say but without any waffle.


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PostPosted: Wed Apr 03, 2013 5:29 pm 
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This is a very good testing question. Probably a discriminator! This is how I would approach it :-

Say the volume of water you start with is 1 unit. When it freezes, it increases in volume by 1/11 of it’s volume. Thus the new volume is 1 + 1/11 or 12/11. When the ice melts, it returns to the original volume of 1, a decrease of 12/11 – 1 = 1/11. However, this time it has decreased 1/11 from a starting point of 12/11. Thus, if you express the decrease of 1/11 as a part of it’s volume, 12/11, it is a matter of dividing 1/11 by 12/11.
1/11 / 12/11 = 1/11 x 11/12 = 1/12

I hope this is not too difficult to follow.
Tagore


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PostPosted: Thu Apr 04, 2013 8:38 am 
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thankyou so much everyone. Its clear to me and now i can explain to DD:-)


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PostPosted: Thu Apr 04, 2013 10:22 am 
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Tagore wrote:
This is a very good testing question. Probably a discriminator! This is how I would approach it :-

Say the volume of water you start with is 1 unit. When it freezes, it increases in volume by 1/11 of it’s volume. Thus the new volume is 1 + 1/11 or 12/11. When the ice melts, it returns to the original volume of 1, a decrease of 12/11 – 1 = 1/11. However, this time it has decreased 1/11 from a starting point of 12/11.
Thus, if you express the decrease of 1/11 as a part of it’s volume, 12/11, it is


and here I would just say that since the denominators are the same (11) its lost 1 out of 12 i.e 1/12


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