lalania1 wrote:

A chemical supply company has 60 liters of a 40% HNO3 solution. How many liters of pure undiluted HNO3 must the chemists add so that the resultant solution is a 50% solution?

A) 12

B) 15

C) 20

D) 24

E) 30

Use weighted Avg:

\(\frac{W1}{W2}=\frac{(A2-Avg)}{(Avg-A1)}\)

Here W1 = 60; W2 is what we need to find.

Avg = 50%; A1 = 40%; A2 = 100%

\(\frac{60}{W2}=\frac{(100-50)}{(50-40)}=\frac{5}{1}\)

W2 = 12

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If you analyze enough data, you can predict the future.....its calculating probability, nothing more!