The ratio of water and alcohol in two different containers is 2:3 and 4:5. In what ratio we are required to mix the mixtures of two containers in order to get the new mixture in which the ratio of alcohol and water be 7:5?

$W1:A1 W2:A2 ..... WN:AN$

  2 : 3                   4 : 5                    5 : 7 

$\frac{W1}{W1+A1} = \frac{2}{5} \frac{W2}{W2+A2}=\frac{4}{9} \frac{WN}{WN+AN} = \frac{5}{12}$

= 72/180

= 80/180

= 75/180  

 =>     5   :   3

Therefore, the ratio is  5: 3