Hi All,

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:

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