<PRE><B>Question 668647</B>
How many liters (L) of a 20% solution must be mixed with 40 L of a 80% solution to get a 50% solution? 
-----
Quantity Equation: x  + 40 = y
Ingrediant Eq::: 0.20x + 0.80*40 = 0.50y
----------------------------------------------
Rearrange and multiply the 1st equation by 20
Rearrange and multiply the 2nd equation by 100
----------------------------------------------
20x - 20y = -800 
20x - 50y = -3200
-------------------
Cheers,
Stan H.
</PRE>