There are 2 possible routes in the morning. A 19 Mile route (which is mainly motorway). Average speed is 60 Mph and the average mpg is 45. Or a 11 route, flat ground but it's mainly city so the average speed is 30Mph and the average mpg is 30. I would like to know which one would be more efficient and how would this be calculated. Thanks.
11 miles divided by 30 (mpg) means you'll use around 0.37 of a gallon.
19 miles divided by 45 (mpg) means you'll use around 0.42 of a gallon.
Time wise, the 19 mile route at 60mph will take you 19 minutes (at 60mph you cover a mile a minute, however in order to obtain an average speed of 60mph over 19 miles you'll find you'll have to touch some very high speeds to counteract being stationary at the beginning and end of the journey).
The 11 mile route at 30mph will take 3 minutes longer, 22 minutes as at 30mph you cover 1 mile every two minutes.
Hopefully this helps answer your question.