getting 62 mpg from £13 fuel, but use a further 9 litres and drops to 50 mpg ?

Did a 180 mile journey today, began with a full tank of fuel, after journey it cost £13 to fill up to brim again, so 13 litres which equates to 62 mpg approx.

However, it would have taken approx. 70 miles more until I was at half fuel point. it takes 22 litres to fill from half to brim. so if calculated, 250 miles at 22 litres of fuel, it would be approx 51 mpg.
so how by driving just 70 more miles using 9 litres more fuel causes my mpg to go from 62 mpg to 51 mpg ?

ty

I fully answered this same question asked by you some time ago (post #14 in this thread):

www.thestudentroom.co.uk/showthread.php?p=60493295&highlight=

Fuel gauges are notoriously inaccurate. Half way mark on the gauge cannot be relied on to indicate the tank is accurately half-full.

Driving in an urban area will not produce the same mpg as driving at a constant speed on a motorway.

Why are you having so much trouble understanding this?

ok, when the gauge is reading half full are you saying there is much more than half left in the tank ?
How is one supposed ot measure mpg if the gauge is not accurate