The ratio of milk and water in a mixture is 7 : 5. How much part of the mixture should be replaced by water so that the ratio of milk and water becomes 2 : 3.

\(\frac{11}{35}\)

     Milk     :     Water

       7       :        5         ............(i)

       2       :        3         ............(ii)

Note: a) if we put out some qty. of mixture from the container, the ratio b/w milk & water always remains same in the remaining qty.

(b) after that if water is replaced, it means milk ratio should be same.

Therefore, (i) × 2 and (ii) × 7, to make the milk equal.

     Milk     :     Water

       14     :        10      

                          ↓ +11 (replaced qty)

       14     :        21     :     35 (Final or Initial qty.)

Therefore 11 part of the total mixture (i.e. 35) replaced ⇒ \(\frac{11}{35}\)