Question

An industrial solvent of 90% strength is prepared and stored in a 150 litres container. The container is filled to 80% of its capacity. It is required to decrease the concentration of the solvent in the container to less than 60%. For doing this, either pure water can be added to it and/or solution can be removed. But removal can only be done if there is no place for adding water. At a given time, only 10 litres of the solution can be added or removed. how many times should water be added to the solution?

• A. 4
• B. 5
• C. 9
• D. 6

Answer 1

The correct option is D 6

Volume of solution in container $=(\frac{4}{5}\times 150)l=120l$
Concentration of solvent $=(\frac{9}{10}\times 120)l=108l$
When first time water is added the concentration of solvent $=\frac{108}{130}\times 100=83\%$
When 2nd time water is added the concentration of solvent $=\frac{108}{140}\times 100=77\%$
When 3rd time water is added the concentration of solvent $=\frac{108}{150}\times 100=72\%$
Now, 10l solution should be removed, solvent present in container = (108-7.2)l = 100.8l
Again 10 l water is water is added and 10 solvent is removed.
To get the required solution, water is added for 6 times.