please help with this question (freezing and melting)

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henna025
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Joined: Sun Dec 09, 2012 2:25 pm

please help with this question (freezing and melting)

Post by henna025 »

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
hermanmunster
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Re: please help with this question

Post by hermanmunster »

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:
stroudydad
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Re: please help with this question

Post by stroudydad »

Removed because my post was more confusing than previously quoted..
WP
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Re: please help with this question

Post by WP »

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.
ginx
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Re: please help with this question (freezing and melting)

Post by ginx »

Beyond me.
stroudydad
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Re: please help with this question (freezing and melting)

Post by stroudydad »

Well put WP, exactly what I tried to say but without any waffle.
Tagore
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Re: please help with this question (freezing and melting)

Post by Tagore »

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
henna025
Posts: 24
Joined: Sun Dec 09, 2012 2:25 pm

Re: please help with this question (freezing and melting)

Post by henna025 »

thankyou so much everyone. Its clear to me and now i can explain to DD:-)
Reading Mum
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Re: please help with this question (freezing and melting)

Post by Reading Mum »

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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