Answer:
18 L
Step-by-step explanation:
Given : she must mix a solution of 67% herbicide with a solution of 46% herbicide to form 42 liters of a 55% solution.
To Find: How much of the 67% solution must she use?
Let x = amount of 67% solution needed
Then 42-x=amount of 46% solution needed
Now we know that the pure herbicide in the 67% solution
So, pure herbicide = (0.67x)
The amount of pure herbicide in the 46% solution (0.46(42-x))
Now 42 liters of a 55% solution = (0.46(42-x))
So,
Amount of 67% solution + Amount of 46% solution = 42 liters of a 55% solution
⇒0.67x+0.46(42-x)=0.55*42
⇒0.67x+19.32-0.46x=23.1
⇒0.21x=3.78
⇒
⇒x = 18 liters
Hence she use 18 liters of the 67% solution