Math IC Problem---need help

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Discus: SAT/ACT Tests and Test Preparation: April 2004 Archive: Math IC Problem---need help
By Phantom (Phantom) on Friday, April 30, 2004 - 06:34 pm: Edit

How do you do this problem? (it's from the Real SAT II's book, Math IC)

A solution is made by mixing concentrate with water. How many liters of concentrate should be mixed with 2 liters of water so that 32 percent of the solution is concentrate?


What I did:
I said that x was the number of liters of concentrate needed. Therefore, 2+x represents the final amount of solution.

Since the 2 L of water have 0% concentrate, and x is 100% concentrate:

2(0) + x = .32 (2+x)

x = 0.64 + 0.32x
0.64x = 0.64
x = 1

However, the answer is not 1. The answer is 0.94.

Can someone help me?

By Starchybean (Starchybean) on Friday, April 30, 2004 - 06:41 pm: Edit

Maybe because 1x - 0.32x does not equal 0.64x. It equals 0.68x. When you divide 0.64 by 0.68 you end up with 0.94.

By Arow (Arow) on Friday, April 30, 2004 - 06:44 pm: Edit

don't they have explanations in that book?

This question is very easy. You just went the wrong direction in finding the answer

Let x be the number of liters of the concentrate you add

Now the equation is: x/(x+2)= 32/100
x= .9411

Easy right? :)

By Phantom (Phantom) on Friday, April 30, 2004 - 07:21 pm: Edit

o god, I'm so stupid. it's mistakes like these that will screw me over tomorrow. sorry for the waste of space.

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