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A pot filled with 1 kilogram of solution contains 7 percent sodium chl

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A pot filled with 1 kilogram of solution contains 7 percent sodium chl  [#permalink]

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New post 17 Oct 2016, 11:12
1
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A
B
C
D
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Question Stats:

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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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Re: A pot filled with 1 kilogram of solution contains 7 percent sodium chl  [#permalink]

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New post 17 Oct 2016, 13:15
alanforde800Maximus wrote:
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.


Solution = 1000
Water = 930
Salt = 70

Quote:
if water is boiled off until the amount of solution has decreased by 30 percent


We know Total Solution ( After Evaporation ) = Water (New) + Salt ( As earlier)

700 = 630 + 70

So, Percentage of Salt = 70/700*100 => 10%

Hence answer will be (C)


PS : Feel free to revert in case of any doubt ...

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Re: A pot filled with 1 kilogram of solution contains 7 percent sodium chl  [#permalink]

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New post 17 Oct 2016, 13:35
1
Case 1
Solution = 1000g
Salt = 70g
water= 1000-70=630g
--------
Case 2(Post Evaporation)

Solution = (1-0.3)*1000=700g
Salt=70g(as evaporation doesn't lead to changes in the quantity of salt)
Water=700-70=630g

Weight% for salt = (70/700)*100
= 10%

Correct option is C
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Re: A pot filled with 1 kilogram of solution contains 7 percent sodium chl  [#permalink]

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New post 25 Jan 2018, 13:54
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%

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Re: A pot filled with 1 kilogram of solution contains 7 percent sodium chl  [#permalink]

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New post 25 Jan 2018, 17:18
alanforde800Maximus wrote:
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%


let x=% of sodium chloride in remaining solution
.07*1=x*.7
x=.07/.7=.10=10%
C
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Re: A pot filled with 1 kilogram of solution contains 7 percent sodium chl   [#permalink] 25 Jan 2018, 17:18
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