Grab a nearby calculator. You're going to have to note down the price of the fuel in pesos, per liter. Next, jot down the exchange rate that was last used to convert your dollars to pesos: Example 7.88 (to 1)
This formula only works if you can remember it's 'key' numbers, so jot them down on the back of a business card and stick it back in your wallet or purse. The calculator is used for simple multiplication and division.
Enter the price per liter (in pesos) ---------example $2.50
Next: Multiply that by 4 (X4)------------------result $10.00
Next: Multiply again, but times 94.64-------then push the % percent key---------result $.9.46
Finally divide by the exchange rate---------------------------------------------result $1.20 (dollars
per gal)
A liter is "close" to being a US quart, but we needed to adjust it for an exact fit. 94.64th of a liter is exactly one quart. Most Mexican dispensing meters are not this accurate.