RJ, Wayne is correct, but may I presume you cannot do those calcs in your head ?

If so desired, try this:

From your example of 40 mpg and 120 mpg, you have used 1 part gasoline pulsing, and 1/3 of that part gliding. 80 divided by 4/3 = 80 * 3/4 = 60 MPG.

R2-E2, 2G Prius.
Highway/City/Husband/Wife MPG: 56.5, as of 12/2005, 26K miles

Jac Nasser, Ford President: "We are planning to launch a hybrid version of
this car [P2000] within this year [1998]. We will also make FCEV available in
2004."