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Q: If in 30 liters of a solution 90 percent is alcohol then how much water needs to b added to make it 80 percent?

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10 liters.

You have 6 litres of alcohol in 24 litres of water You need to add x litres to make 6 equal to 15% of 30 + x. 6 is 15% of 40, so x = 10

4 litres

Let L be the liters to be added. Then (L) x (0.2) + (40 x 0.9) = (L + 40) x 0.6 0.2L + 36 = 0.6L + 24 36 - 24 = (0.6 - 0.2)L 12 = 0.4L L = 12/0.4 = 120/4 = 30 Liters

75 litres

684 ml

4.5 litres of a 30% solution to the appropriate quantity of the 90% solution.

There are 3 litres of alcohol in your starting mixture of 4 litres. If you add 6 litres of water you will have 3 litres of alcohol in a total of 10 litres. This is the required strength.

2%

About 80ml of water must be added to 40ml of a 25 percent by weight solution to make a 2 percent by weight solution.

About 80ml of water must be added to 40ml of a 25 percent by weight solution to make a 2 percent by weight solution.

2 litersLet X represent the amount of pure alcohol to be added to the 7 liters of 10% alcohol solution to get a 30% alcohol solution. We want .3(7+x)=.1*7+x [because we need the alcohol in the final solution to equal the amount of alcohol in the original solution plus the amount of alcohol we are adding). Solving for x, we get:.3(7+x)=.1*7+x2.1+.3x=.7+x1.4=.7x2=xThus, 2 liters of pure alcohol needs to be added to the solution.Added noteto deal with the so called 'dilution contraction' of total volumeIf it were % by MASS ( %m/m), it's quite easy to do (based on the 'Mass Conservation Law). You calculate with mass (kg) and mass-% (%m/m) i.s.o. volume (L) and vol% (%v/v).However if the meaning was: % by Volume ( %v/v) then calculation appears to become quite complicated, but not impossible if you know at least the density values of all solutions (original 100%v/v or 10%v/v and final 30%v/v).DO NOT use: (orig. volume) + (added volume) = final volume, as done above, if exact figures are necessary.It's only a rule of thump, an approximation. This is because fluids can contract on mixing at dilution. There is no rule such as: conservation of volume.Your case: 7 L + 2 L (is not equal but) < 9 L final solution.

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