Question

At Edhelper Gas, regular gas is $1.29 per gallon and ultra gas is $1.80 per gallon. If Edhelper gas sold $69.99 worth of regular, how many gallons of ultra must be sold to have an average selling price of $1.603 per gallon.

Answer 1

1.29x = 69.99
x = 69.99/1.29 = 54.26
(1.29x + 1.80y)÷(x+y) = 1.603
(69.99 + 1.80y)÷(54.26+y) = 1.603
69.99 + 1.80y = 1.603y + 86.97
1.80y - 1.603y = 86.97 - 69.99
0.197y = 16.98
0.197y/0.197 = 16.98/0.197
y = 86.20 gallons of ultra

Answer 2

Let g represent the number of gallons of ultra.
.. 1.603 = (1.80g +69.99)/(g +69.99/1.29)
.. 1.603(g +69.99/1.29) = 1.80g +69.99
.. 1.603(1.29g +69.99) = 1.29(1.80g +69.99)
.. 69.99(1.603 -1.29) = 1.29g(1.80 -1.603)
.. g = 69.99*(1.603 -1.29)/(1.29*(1.80 -1.603))
.. g ≈ 86.203

Edhelper Gas must sell 86.203 gallons of ultra to make the average selling price 1.603.