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A pot filled with 1 kilogram of solution contains 7 percent

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A pot filled with 1 kilogram of solution contains 7 percent

by alanforde800Maximus » Mon Oct 17, 2016 10:13 am
A pot filled with 1 kilogram of solution contains 7 percent sodium chloride by weight in water. if water is boiled off until the amount of solution has decreased by 30 percent, the remaining solution will be approximately what percent sodium chloride by weight?

a) 4.28%
b) 7%
c) 10%
d) 21%
e) 90%

Please assist with above problem.
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by [email protected] » Mon Oct 17, 2016 10:33 am
Hi alanforde800Maximus,

When dealing with these types of questions, it often helps to break the mixture down into it's 'pieces'

We're told that 1 kg solution is 7% sodium chloride. Thus the mix is...

.07 kg sodium chloride
.93 kg water

We're told that the solution is decreased by 30% (water is boiled off until we get to that weight, but the amount of sodium chloride stays the same), so the new mix is...

1 - (.3)(1) = .7 kg solution

.07 kg sodium chloride
.63 kg water

With this new mix, the percent that is sodium chloride is .07/.7 = 10%

Final Answer: C

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