Question 478508
you have 12 1/2 gallons of gas and us use 1/5 of the gas how much gas do you have left? 
Begin by changing 12 1/2 gals into an improper fraction:
12 + 1/2
24/2 + 1/2
25/2
.
Next, if you've used 1/5, there is 4/5 left so:
(4/5)(25/2) = 100/10 = 10 gallons (amount of gasoline left)