SOLUTION: A chemist has two alloys, one of which is 20% gold and 15% lead and the other which is 40% gold and 50% lead. How many grams of each of the two alloys should be used to make an all

Let x be the amount of the first alloy (in grams)
and y be the amount of the first alloy.


Then your system of equations is

0.2*x + 0.4*y = 104    (1)    (providing the required content of gold)
0.15x + 0.5*y =  84    (2)    (providing the required content of lead)


Solve the system.  The elimination method is preferred.