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Just referring to Performance Final Exam Q36 for distance to PNR question.
The answer given states that to find PNR is: 64L x 190kts divided by 340kts=36mins.
Just wanted to clarify why we use 64litres in this calculation and not the equivalent figure in minutes?
In the case of this question, the cruise fuel consumption happens to be 60 litres/hr. That's one litre per minute. Since the trip fuel is 64 iitres, the safe endurance is 64 minutes (64 litres @ 60 litres/hour). The formula says Time to PNR = 64 x 190 ÷ 340. The 64 is minutes, it just happens also be 64 litres in this case.
Bob