Given a
liters of 35%
alcohol solution, and b
liters of 60%
alcohol solution, what would be the alcohol ratio after we'll mix this two solutions?
The a
liters are actually a*35/100
alcohol, and a*(1-(35/100))
water. Likewise the b
liters contains b*60/100
alcohol and b*(1-(60/100))
water.
Mixing them together would give us a*35/100+b*60/100
alcohol and a*(1-(35/100))+b*(1-(60/100))
water. The question is for which a,b
we have the ratio
((a*35+b*60)/100)/((a*65+b*40)/100) = 50% = 1/2
or
(a*35+b*60)/(a*65+b*40) = 1/2
I believe you can take it from here...