Beginning with a tank containing 8075 gallons of gasoline, more gas is added at a rate of 5 gallons per minute, while alcohol is added at a rate of 10 gallons per minute. When the mixture is 10% alcohol, how many gallons of the mixture are in the tank?
Is there an easier way to do it than writing out every number and making a table, I'm pretty sure there is, but I can't remember it.
An easier way is algebra.
Beginning at time t=0, the amount of gasoline in the tank In gallons) is
G = 8075 + 5 t
and the amount of alcohol is
A = 10 t.
The mixture is 10% alcohol when
A /(G + A) = 0.1 or
G = 9 A.
So, solve this equation for t:
8075 + 5 t = 90 t
85t = 8075
t = 95 minutes.