Let x be the volume of 20% solution in the tank after the given process
Let y be the volume of 100% solution used.
The sum of x and y needs to be equal to the final volume 275L:
The amount of substance (salt) in each solution is calculated by multipliying the volume by the concentration (in decimals); then, the amount of salt in 20% solution is 0.2x, in 100% solution is 1y and in the final solution (45%) is 0.45(275).
Sum amount in 20% solution with amount in 100% solution to get the amount in final solution:
Use the next system of equations to answer the question:
1. Solve x in the first equation:
2. Use the value of x (step 1) in the second equation:
3. Solve y:
The volume of 100% solution that needs to be used is 85.9 Litres.
Then, the litres that must be replaced with 100% solution to produce a full tank with 45% saline solution is 85.9