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can this be solved using weighted average method???

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Bunuel
Eight liters of a 45% saline solution is left in the sun. Water evaporates from the solution leaving a 60% saline solution. Approximately how much water evaporated from the solution?

A. 1.2 liters
B. 2.0 liters
C. 2.1 liters
D. 6.0 liters
E. 7.0 liters

We are given that an 8-liter saline solution is 45% salt (and thus 55% water). Thus:

Amount of salt = 8 x 0.45 = 3.6 liters

Amount of water = 8 - 3.6 = 4.4 liters

We are also given that some amount of solution evaporates, leaving a 60% saline solution. However, since only water evaporates (salt doesn’t evaporate), we can let w be the amount of water that evaporates, and the new solution is 60% = 6/10 = 3/5 saline.

Let’s determine how much water evaporated.

3.6/(8 - w) = 3/5

5(3.6) = 3(8 - w)

18 = 24 - 3w

3w = 6

w = 2

Answer: B
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Bunuel
Eight liters of a 45% saline solution is left in the sun. Water evaporates from the solution leaving a 60% saline solution. Approximately how much water evaporated from the solution?

A. 1.2 liters
B. 2.0 liters
C. 2.1 liters
D. 6.0 liters
E. 7.0 liters


KarishmaB can you pls show how to solve this problem with alligation method :)
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Bunuel
Eight liters of a 45% saline solution is left in the sun. Water evaporates from the solution leaving a 60% saline solution. Approximately how much water evaporated from the solution?

A. 1.2 liters
B. 2.0 liters
C. 2.1 liters
D. 6.0 liters
E. 7.0 liters


KarishmaB can you pls show how to solve this problem with alligation method :)

"Alligation method" for me is the formula:

\(\frac{w1}{w2} = \frac{(A2 - Aavg)}{(Aavg - A1)}\)

It is the easiest way to solve weighted averages problems in most cases. The diagram could get confusing but the formula works very well.

0% and 60% were mixed together to give 45% saline solution.

\(\frac{w1}{w2} = \frac{(60 - 45)}{(45 - 0)} = \frac{1}{3} \)

So pure water : 60% saline = 1 : 3
Since total was 8 ltrs, it means 2 ltrs of water evaporated and left 6 ltrs of 60% saline.

Answer (B)
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