Question 716553
Amount of mixture or resulting solution is V.

Let x amount of 50% and  let y amount of 20%,


{{{(50x+20y)/V=25}}} and {{{x+y=V}}}


For convenience you can choose V as 1 or V as 100 or you can choose V as any value you want for the size of the resulting solution.  V is any size you want or need it to be.