mpg combined

[ligertigon]

Does anyone know how to work out the combined mpg from the following data:

Simulated urban driving: 42.8 mpg

At constant speed of 56mph: 67.3 mpg

At constant speed of 75 mph: 48.7 mpg

I reckon its the average of all 3? or am I missing something? I got this info from an official Toyota manual for a diesel corolla.
I can't source any other mpg figures from anywhere.

Having a problem with some bureaucrats in eire as I am paying tax according to mpg/CO2



re: post below
I cant respond

any idea what the standard ratio is then anyway?

[bobhatton]

Would you not need to know how many miles for each one from a total of 100%

Say
60% at 42.8

30% at 56

10% at 48.7



Bob