Presently a mixture in a tub contains substances A and B in the ratio of 7:5. If 9 litres of this solution is drawn out and B is added to the mixture in certain quantity the resulting mixture becomes 7:9. How much litres of liquid A was kept in the tub initially? Choose the correct choice from the following choices:  A) 87  B) 265  C) 88  D) 21  E) 91
Explanation:   Currently the mixture is in ratio of A/B: 7:5   =&gt; This means fraction of A in the solution: 7/12   =&gt; Fraction of B in the solvent: 5/12   =&gt;New concentration of A= 7-(7/12)9   =&gt;New concentration of B= 5-(5/12)9+x   =&gt; (7-(7/12)9)/(5-(5/12)9+x) = 7/9   =&gt;x=21   ANSWER: 21
<result>D</result>
Presently a mixture in a tub contains substances A and B in the ratio of 7:5. If 9 litres of this solution is drawn out and B is added to the mixture in certain quantity the resulting mixture becomes 7:9. How much litres of liquid A was kept in the tub initially?