Question 761012
The value for the quantity removed is equal to the value for the quantity added.  Call this quantity, v, the liters both of the 40% antifreeze removed and of the pure antifreeze added.


{{{15*40-v*40+v*100}}} represents the amount of pure antifreeze in the resulting adjusted 15 liter capacity cooling system.  The volume of the mixture will be the same as it was before the adjustment.  The pure antifreeze material is 100% antifreeze.


{{{highlight((15*40-v*40+v*100)/15=50)}}}
{{{(15*40+(100-40)v)/15=50}}}
{{{(15*40+60*v)/15=50}}}
Solve for v.