ggarr wrote:

a 30% solution of alcohol is mixed with a 50% solution of alcohol to form a 10 liter solution of 45% alchohol. How much of the 30% solution was used.

2.0 liters

2.5 liters

2.7 liters

3.0 liters

3.2 liters

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I'm doing this and coming up empty.

30(L)/100 + 50(10-L)/100 = (10)45/100

It is actually quite simple. You want to find the ratio/weighted for each:

the answer should be B

dunno if I can explain this well.. there were these 'killer' notes that killersquirrel provided some time ago

30% + 50 % = 45% of a 10 liter solution

ratio of 30% : 50% ---> 1 : 3

so 30% = 1/4 or 25% of 10L solution = 2.5L