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 Posted: Wed Apr 03, 2013 2:18 pm

Joined: Sun Dec 09, 2012 1:25 pm
Posts: 24
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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Joined: Fri Sep 15, 2006 8:51 am
Posts: 8598
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

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Joined: Sat Oct 08, 2011 1:25 pm
Posts: 1493
Removed because my post was more confusing than previously quoted..

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Joined: Thu Jan 03, 2008 8:26 am
Posts: 1330
Location: Watford, Herts
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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 Posted: Wed Apr 03, 2013 4:44 pm

Joined: Mon Jul 04, 2011 1:47 pm
Posts: 2151
Location: Warwickshire
Beyond me.

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 Posted: Wed Apr 03, 2013 4:56 pm

Joined: Sat Oct 08, 2011 1:25 pm
Posts: 1493
Well put WP, exactly what I tried to say but without any waffle.

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 Posted: Wed Apr 03, 2013 5:29 pm

Joined: Thu Jun 14, 2012 9:28 am
Posts: 121
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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 Posted: Thu Apr 04, 2013 8:38 am

Joined: Sun Dec 09, 2012 1:25 pm
Posts: 24
thankyou so much everyone. Its clear to me and now i can explain to DD:-)

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 Posted: Thu Apr 04, 2013 10:22 am

Joined: Tue Oct 04, 2011 8:44 am
Posts: 1497
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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