How much premium gas (92 octane) and regular (87 octane) should be mixed to obtain 50 gallons of mid grade (89 octane?)

Question

 How much premium gas (92 octane) and regular (87 octane) should be mixed to obtain 50 gallons of mid grade (89 octane?)

Answer 1

Octane is a rating - not a measure. 

Ignoring that 

92(50 - x) + 87x = 89(50)

4750 - 92x + 87x = 4450

-92x + 87x = -300

 

You can complete the solution.