sujoykrdatta wrote:
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:
A) 100
B) 150
C) 180
D) 200
E) 240
Percentage of indigo in bottles 1 and 2: 33% and 17% respectively.
A part of the solution (say y cc) from the first bottle is thrown away and replaced by an equal volume (y cc) of the solution from the second bottle
Thus, in the first bottle, there is a mix of 33% indigo (say x cc) with 17% indigo (y cc) => the resultant solution has 21% indigo.
(33x + 17y)/(x + y) = 21
=> 12x = 4y
=> x : y = 1 : 3
Since the total volume is 800cc, we have: y = [3/(1+3)] x 800 = 600 cc
Thus, 600 cc of solution from bottle 2 was moved to bottle 1.
Thus, volume remaining in bottle 1 = 800 - 600 = 200 cc
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Answer D