Answer :
Let x be the 10% solution and y be the 4% solution.
.1x + .04y = .07(4)
x + y = 4
These are the two equations.
Solve the equations.
.6y = 1.2
y = 2
Plug this back into the second equation to get x = 2.
Therefore the Chemist must mix 2 liters of the 10% solution with 2 liters of the 4% solution to get 4 liters of the 7% solution.
.1x + .04y = .07(4)
x + y = 4
These are the two equations.
Solve the equations.
.6y = 1.2
y = 2
Plug this back into the second equation to get x = 2.
Therefore the Chemist must mix 2 liters of the 10% solution with 2 liters of the 4% solution to get 4 liters of the 7% solution.