My ford focus is taking less gas?

I bought a 09 ford focus a month ago and a full tank was 374miles until E. Then the next time i filled it up, i put premium in it. Then the next time i went to the gas station, i had 103miles until E, so i asked to put $24 of Regular 87 octane gas in my car. My car only took $18 worth and i only had 268miles until E. Did the premium gas have an effect on my car?

No - that is NOT how you calculate miles per gallon - you have to log miles driven and exact amount of fuel consumed on a fill-up and do the math, reset the trip meter and repeat for about 10 fill ups and you will have an avg mpg - then switch fuel grades and do another 10 fill-ups and do the math again - random fill-ups mean nothing.

The has prices went down Numbskull. Check the gallons. Not the cost of the tank

No, you are just keenly observing the shortcomings of those range estimators. All OBDII cars had them internally, but now they are just displaying the calculations on the dashboard for convenience. They are based on electrical resistance incoming from the fuel level sender. Those units are far from perfect, so estimate your mileage by dividing miles driven by number of gallons accepted (filled up). Premium is just designed for high compression and turbo engines, to increase performance. It won't increase mileage on a normal engine that doesn't call for it, and it is no cleaner or better in any other way. In America, we usually add more ethanol to premium blends, which raises octance, and lowers the energy contained by the fuel (less mileage). Trust the engineers who wrote your owners manual.

Premium gas is a higher octane which burns hotter. Burns hotter means more explosive force in the cylinder. Therefore more power per gallon of fuel. More miles per gallon.

You need to actually figure out the mileage by dividing the amount of gallons into the miles driven each time. Just going by the price and miles driven isn't accurate enough to tell you anything.