Russ wrote:
How do I program excel to read a "mpg" value in one cell and display its
conversion to "l/100 km" in another cell? (ie. how would the conversion
formula be written)?

You need to know if it is an English gallon or a US gallon (they are
different).
1 mile is 1.6 km
1 English (Imperial) gallon is 4.546 litres
1 US gallon is 3.785 litres
(you can get both of these conversions easily from google)
Let's assume we are working in Imperial units
30 miles per gallons works out at 30*1.6 km/4.546 litre = 10.559
km/litre
Therefore if we take the reciprocal of the last result we get 0.0947
litres/km, so to get it in units of litres/100 km we need to multiply
by 100 to get: 9.47 litres/100 km.
(The calculation using US gallons is obviously just as easy)

Hope this helps
Ian Taylor
http://www.iantaylor.org.uk/