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# a 30% solution of alcohol is mixed with a 50% solution of

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Senior Manager
Joined: 14 Jun 2007
Posts: 399
Followers: 1

Kudos [?]: 10 [0], given: 0

a 30% solution of alcohol is mixed with a 50% solution of [#permalink]  17 Jul 2007, 13:22
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0% (00:00) correct 100% (00:00) wrong based on 4 sessions
a 30% solution of alcohol is mixed with a 50% solution of alcohol to form a 10 liter solution of 45% alchohol. How much of the 30% solution was used.
:SPOILER BELOW LINE::

2.0 liters
2.5 liters
2.7 liters
3.0 liters
3.2 liters

_______________________________________-

so i was able to find the answer; but how do i know which solution to assign the 10-x variable to (other than trial and error)

i.e.

but 30%(10-x) +50%(x)... leads you to 7.5. Obviously that isn't in the answer choices, so I switched them, but it wasted valuable time
Director
Joined: 26 Feb 2006
Posts: 905
Followers: 4

Kudos [?]: 52 [0], given: 0

Re: PS - mixture problem - question about assigning variable [#permalink]  17 Jul 2007, 13:36
you were correct in both cases but you defined both as x where as you need to difine which is x and is (10-x)?

suppose: x = 30% solution
30% x + 50% (10 - x) = 45%
x = 2.5 liters.

suppose: x = 50% solution
then 30% solution = 10 - x

30% (10-x) + 50% x = 45%
x = 7.5 liters.
then 30% solution = 10 - x = 2.5 liters.

hth
Senior Manager
Joined: 14 Jun 2007
Posts: 399
Followers: 1

Kudos [?]: 10 [0], given: 0

Re: PS - mixture problem - question about assigning variable [#permalink]  17 Jul 2007, 13:45
Himalayan wrote:
you were correct in both cases but you defined both as x where as you need to difine which is x and is (10-x)?

suppose: x = 30% solution
30% x + 50% (10 - x) = 45%
x = 2.5 liters.

suppose: x = 50% solution
then 30% solution = 10 - x

30% (10-x) + 50% x = 45%
x = 7.5 liters.
then 30% solution = 10 - x = 2.5 liters.

hth

oohhh... yeah... ::duh::

thank you himalayan. it is easy to lose track when you are rushing like crazy.... and it is hard to keep very detailed notes when you are working a problem. i thought i was losing my mind for a second...
Re: PS - mixture problem - question about assigning variable   [#permalink] 17 Jul 2007, 13:45
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