fuel price calibration

[coley13]

i'm not very good at math but.

if fuel was $1.00 a litre for $20 you would get 20 litres

at $2.00 a litre for $20 you would get 10 litres

$1.50 a litre for $20 you would get 15 litres

at $1.43 i only got 13 litres. should'nt i have got more than 15 litres. is there something i'm not working out properly. as i said i'm not very good at maths. am i doing my head in for nothing or are the petrol bowsers not calibrated properly