The volume of a brass piece is twice that of a aluminium piece the total weight of both piece is 1280g if the weight of 1 cu cm of aluminum is 7..8g and that of a brass is 8.9g find the volume of each piece

Answer : 

Let Volume of brass piece  =  x 
And
Volume of Aluminium piece  = y
So according to first condition we get 

x  =  2y                                                          ------------------  ( 1 ) 

And from second condition we get 

x ( 8.9 )  + y  ( 7.8 )  =  1280 

From equation 1 we get 

2y ( 8.9 ) + y ( 7.8 ) =  1280 

17.8y + 7.8y  = 1280

25.6y  = 1280 

y  = 50   , substitute that value in equation 1 , we get 

x = 2 ( 50 )  =  100 
SO,
Volume of Brass piece  =  100 cm³ 
And
Volume of Aluminium piece  =  50 cm³                          ( Ans )