Question 24730

Since 30% = 30x
Since 10 gallon of 50% = 50(10-x) 
Total = 40(10)
Add it together:
30x+50(10-x)=40(10)
30x+500-50x=400
-20x=-100
x = 5
Hence, there should be about 5 gallons of 30%.
Paul.