Percentages Question 5 - CAT 2021
The strength of an indigo solution in percentage is equal to the amount of indigo in grams per 100 cc of water. Two 800 cc bottles are filled with indigo solutions of strengths 33% and 17%, respectively. A part of the solution from the first bottle is thrown away and replaced by an equal volume of the solution from the second bottle. If the strength of the indigo solution in the first bottle has now changed to 21%, then the volume, in cc, of the solution left in the second bottle is
Step-by-Step Explanation
Bottle A contains a 33% solution and Bottle B contains a 17% solution.
After mixing, Bottle A becomes a 21% solution.
Using the rule of alligation,
A : B = (21 − 17) / (33 − 21) = 4 / 12 = 1 : 3
Thus, one part of Bottle A is mixed with three parts of Bottle B.
Since each bottle initially contains 800 cc, the volume transferred from Bottle B is
3 / 4 × 800 = 600 cc
Therefore, the solution left in Bottle B is
800 − 600 = 200 cc
Hence, the correct answer is 200 cc.
💡 FundaMakers Tip: Whenever two solutions are mixed to obtain a new concentration, Alligation is often the fastest method.