Help! horrid word problems?

Question

How many liters of pure alcohol must be added to 20 liters of a 40% solution to obtain a 60% solution?

Answer 1

I think this is a trick question, but let's start by pretending there is no trick.

20 liters of a 40% alcohol solution would be 60% water, so there would be 12 liters of water.

The final solution is 60% alcohol and 40% water, and it will still have 12 liters of water. If 12 liters are 40% of the total volume, then the total volume is 12 liters / 40% = 30 liters.

To produce 30 liters of total solution, you need to add 10 liters to the 20 liters you already have.

But I say that it is a trick question because I've been told that mixing alcohol and water results in a total volume slightly less than the sum of the volumes of alcohol and water. But I don't know how much, and you would need that information to solve the problem.

Unless this is an advanced chemistry or physics class, you should probably treat it as a straightforward problem whose solution is: 10 liters.

Answer 2

As said above, if you mix two measured volumes of water and alcohol together, you will not end up with a total equal to the two volumes added together. Assuming that is not being asked for, which is by no means certain;


40% of 20 liters by vol. is 8 liters.

You want to increase the percentage by half again as much as is already in the solution.

If you add 4 liters however, you now have 24 liters with 12 liters of alcohol, so you have only achieved 50%, not 60%.

In order to achieve 60% you need to add 16 liters of alcohol, and will have a total of 40 liters of solution containing 24 liters of alcohol.

So if the question really concerns starting with 20 liters and adding alcohol until you have gone from 40% to 60 %, that is how it works. You would add progressively greater and greater amounts of alcohol as you approach but never reach 100%

Now, if the question was just to find how much alcohol was in the original 20 liters (8) and how much it would take to produce 20 liters of 60% solution, the answer would be 12. It is always very important to read exactly what is given and what is required as an answer.

Answer 3

LETS see. .4 * 20 = 8 we need to increase by 50% so add 4L
if 8=.4 than 12 (150% of 8) = 60% or 4 more Ls

Answer 4

2 liters

Answer 5

1.621 with the bar over 621 liters- use value quantity total

Answer 6

i think it is 10L but could be wrong