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S2: By weight the alloy is 6 parts lead and 5 parts copper Alloy is y parts T x be the multiplier 6x+5x+yx=56 11x+yx=56 y,x can have many values. Not sufficient.

A certain alloy contains Lead , copper and tin. how many pounds of tin are in 56 pounds of the alloy

S1 By weight the alloy is 3/7 lead and 5/14 copper

S2 By weight the alloy is 6 parts lead and 5 parts copper

A certain alloy contains Lead , copper and tin. How many pounds of tin are in 56 pounds of the alloy?

(1) By weight the alloy is 3/7 lead and 5/14 copper --> by weight tin will be 1-(3/7+5/14)=3/14 of the alloy, thus there are 56*3/14=12 pounds of tin in the alloy. Sufficient.

(2) By weight the alloy is 6 parts lead and 5 parts copper. Clearly insufficient: for example tin could be 9 parts (45% of 56 pounds) or 89 part (89% of 56 pounds). Not sufficient.

Please explain this, especially the underlined portion :

By weight the alloy is 6 parts lead and 5 parts copper. Clearly insufficient: for example tin could be 9 parts (45% of 56 pounds) or 89 part (89% of 56 pounds).

Regards, Subhash
_________________

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Please explain this, especially the underlined portion :

By weight the alloy is 6 parts lead and 5 parts copper. Clearly insufficient: for example tin could be 9 parts (45% of 56 pounds) or 89 part (89% of 56 pounds).

Regards, Subhash

"By weight the alloy is 6 parts lead and 5 parts copper" means that the ratio lead/copper=6/5, as we don't know how many parts of tin are there then we can not find weight of each. Consider examples: if lead/copper/tin=6/5/9 --> total 20 parts --> tin=9/20=45% of 56 pounds or if lead/copper/tin=6/5/89 --> total 100 parts --> tin=89/100=89% of 56 pounds.
_________________

Please explain this, especially the underlined portion :

By weight the alloy is 6 parts lead and 5 parts copper. Clearly insufficient: for example tin could be 9 parts (45% of 56 pounds) or 89 part (89% of 56 pounds).

Regards, Subhash

If Tin is 9 Parts; then the alloy will be 9 Part TIN+ 6 Parts Lead+ 5 Parts copper = 20 Tin's presence in the alloy will be: 9/20*100 = 45% (45% of the 56 lbs alloy is TIN = 56*45/100 = 25.2 lbs will be TIN)

If Tin is 89 Parts; then the alloy will be 89 Part TIN+ 6 Parts Lead+ 5 Parts copper = 100 Tin's presence in the alloy will be: 89/100*100 = 89% (89% of the 56 lbs alloy is TIN = 56*89/100 = 49.84lbs will be TIN)

Likewise; there will be infinitely many possibilities for TIN's weight in the alloy and exact weight of Tin can't be determined.
_________________

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24 Sep 2013, 18:43

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Re: A certain alloy contains Lead, copper and tin. How many poun [#permalink]

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28 Nov 2014, 23:30

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Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos).

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II: By weight the alloy is 6 parts lead and 5 parts copper

Let Alloy have y parts of tin.

x be the multiplier

\(6x+5x+yx=56\) \(11x+yx=56\) \((11+y)x=56\)

\(y,x\) can have multiples values namely \((45, 1), (17, 2) and (3, 4).\)

Statement II is Not sufficient.

Thus A is the answer. _________________

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