Lisa start her trip with 11 1/2 of gallons of gas in her cars Gas tank she bought an additional 6 4/5 gallons on her trip in and arrived back home with 3 3/10 gallons left how much gas does she use on her trip

She uses 15 gallons of gas.

11 1/2 + 6 4/5 =

23/2 + 34/5 =

115/10 + 68/10 =

183/10 =

183/10 - 3 3/10 =

183/10 - 33/10 =

150/10 =

15

Quantity of gas in the tank with which Lisa started her journey = 11 1/2 gallons

= 23/2 gallons

Quantity of gas additionally bought by Lisa during her trip = 6 4/5 gallons

= 34/5 gallons

Quantity of gas still left in the car after Lisa completed her trip = 3 3/10 gallons

= 33/10 gallons

Then

Quantity of gas used by Lisa during her trip = [ (23/2) + (34/5) ] - (33/10) gallons

= [ (115 + 68) / 10] - (33/10) gallons

= (183/10) - (33/10) gallons

= 150/10 gallons

= 15 gallons

So we can see from the above deduction that Lisa used 15 gallons of gas during her trip. I hope the procedure is simple enough for you to understand.