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by gmatnmein2010 » Sat Feb 20, 2010 3:44 am
A ten-gram piece of a certain alloy contains only gold and silver. If the piece currently contains exactly 3 grams of silver, how many more grams of gold must be added to the piece so that the resulting piece is 10 percent silver?


1)30


2)27


3)25


4)20


5)17
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by ajith » Sat Feb 20, 2010 3:47 am
gmatnmein2010 wrote:A ten-gram piece of a certain alloy contains only gold and silver. If the piece currently contains exactly 3 grams of silver, how many more grams of gold must be added to the piece so that the resulting piece is 10 percent silver?


1)30


2)27


3)25


4)20


5)17
Currently the alloy has 3 grams of silver and 7 grams of gold

now we want to make it 10% silver
10% silver is 3 grams
total weight of the alloy piece would be 30 grams

we need to add 30-10 = 20 grams of gold
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by shashank.ism » Sat Feb 20, 2010 8:51 am
gmatnmein2010 wrote:A ten-gram piece of a certain alloy contains only gold and silver. If the piece currently contains exactly 3 grams of silver, how many more grams of gold must be added to the piece so that the resulting piece is 10 percent silver?
1)30
2)27
3)25
4)20
5)17
10 g alloy = 3g silver + 7g gold
let x g gold be added...so x+10 g alloy = 3g silver + (x+7)g gold
3/(x+10) = 0.1 --> 30 = x+10 --> [spoiler]x= 20 Ans 4[/spoiler]
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by thephoenix » Sat Feb 20, 2010 9:11 am
gmatnmein2010 wrote:A ten-gram piece of a certain alloy contains only gold and silver. If the piece currently contains exactly 3 grams of silver, how many more grams of gold must be added to the piece so that the resulting piece is 10 percent silver?


1)30


2)27


3)25


4)20


5)17
If the ten-gram piece contains 3 grams of silver, then it must also contain 7 grams of gold.
NOW WHEN X gm of gold added; silver becomes 10% of total
since in total wt final wt. of silver is 3----> total=30 gms
so after addition of x total gold =27 gms
initially 7 gms was there so added=20 gms
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