X and Y are two alloys of copper and aluminium prepared by mixing the metals in the ratio 6 : 5 and 5 : 9, respectively. If equal quantities of the alloys are melted to form a third alloy Z, what ratio of copper and aluminium will be in Z?

139 : 169

       Cu    :    Al

X     6      :     5

Y     5      :     9

When equal quantity of both mixtures is mixed together

     Cu    :    Al                     Total

X    ( 6     :     5     =         11 ) x 14

Y    ( 5      :    9     =         14 ) x 11

—————————————

X    84     :     70            

Y    55      :    99     

—————————————

      139    :    169       

The ratio of copper and alumininum in alloy Z  is

     139       :      169