Answer:
<u>800 liters</u> of 90% saline solution and <u>1200 liters</u> of 40% saline solution should be used.
Step-by-step explanation:
Given:
At 2000 liters of 60% saline solution the attendant has to mix a 90% and a 40% saline solution.
Now, to find the number of liters of saline solution each should be used.
<u><em>Let the liters of 90% saline solution mix be </em></u>
<u><em /></u>
<u><em>And let the liters of 40% saline solution mix be</em></u> 
So, the total number of liters:


Now, the total percentage of saline solution:



Substituting the value of
from equation (1) we get:



Subtracting both sides by 800 we get:

Dividing both sides by 0.5 we get:

<u>The liters of 90% saline solution mix = 800.</u>
Now, substituting the value of
in equation (1) to get the liters of 40% saline solution:



<u>Thus, the liters of 40% saline solution = 1200.</u>
Therefore, 800 liters of 90% saline solution and 1200 liters of 40% saline solution should be used.