How many liters of a 50% solution should be mixed with 80 liters of a 20% solution to get a 40% solution of some substance?

To solve this problem, we need to perform the following actions:
Let’s designate the quantity of the first solution for x.
The volume of the first substance is 0.5x.
Second 0.2 * 80 = 16 liters.
Then the result of mixing will be: (x + 80), and the volume of the substance: 0.4 (x + 80).
Let’s write the equation: 0.5x + 16 = 0.4 (x + 80).
Let’s solve it: 0.5x – 0.4 x = 32-16, x = 160L
As a result of the actions taken, we get the answer to the problem: 160 liters.