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mehaksal: Master | Next Rank: 500 Posts; Posts: 122; Joined: Tue Jul 10, 2012 9:12 am; Thanked: 2 times; Followed by:8 members

C right?!!

by mehaksal » Wed Aug 08, 2012 3:43 am

X grams of water were added to the 80 grams of a strong solution of acid. As a result, the concentration of acid in the solution became 1/Y times of the initial concentration. What was the concentration of acid in the original solution?

1. X=80
2. Y=2

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Source: Beat The GMAT — Data Sufficiency | Wed Aug 08, 2012 3:43 am

anujan007: Senior | Next Rank: 100 Posts; Posts: 57; Joined: Sat May 15, 2010 5:46 am; Thanked: 2 times

by anujan007 » Wed Aug 08, 2012 5:54 am

Let us consider the first statement.

(i). X=80 but no information given on Y hence insufficient.

(ii). Y=2 but no information given on X hence insufficient.

Considering both statements together --:

original acid solution's weight = 80
80 Grams of water were added. Hence new weight of the acid solution is = 160

Consider original conc of water as w. Hence new concentration is (w+x)

Consider original conc of acid as a. Hence new concentration is (a/2)

w + a = 80 ----> (I)

after the addition of 80 gms water,

(w+x) + (y/2) = 160 ---> (II)

There are 4 variables and 2 equations hence both together are not sufficient.

The answer I would choose is E.

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Bill@VeritasPrep: GMAT Instructor; Posts: 1248; Joined: Thu Mar 29, 2012 2:57 pm; Location: Everywhere; Thanked: 503 times; Followed by:192 members; GMAT Score:780

by Bill@VeritasPrep » Wed Aug 08, 2012 7:15 am

anujan007 wrote:Let us consider the first statement.

(i). X=80 but no information given on Y hence insufficient.

(ii). Y=2 but no information given on X hence insufficient.

Considering both statements together --:

original acid solution's weight = 80
80 Grams of water were added. Hence new weight of the acid solution is = 160

Consider original conc of water as w. Hence new concentration is (w+x)

Consider original conc of acid as a. Hence new concentration is (a/2)

w + a = 80 ----> (I)

after the addition of 80 gms water,

(w+x) + (y/2) = 160 ---> (II)

There are 4 variables and 2 equations hence both together are not sufficient.

The answer I would choose is E.

Agreed. Any original concentration will be cut in half by the addition of 80 grams of acid.

If it was originally 1/80, it's now 1/60. If it was originally 4/80, it's now 4/160. We can never find an exact value.

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