Note: The answer here is unconfirmed at the moment, and whilst it is a simple question to calculate, there may be more to the question that has not been fed back to us, such as a policy not to interpolate or to take the most conservative figures, etc. We have chosen to add that interpolation should be used to avoid confusion, but please read the question carefully in the real exam to make your own judgement of what the question requires, it may well be different. Please let us know if you see this question and remember anything about it from the real exam, thank you!

The trip fuel is calculated for a flight based on its expected routing, winds, cruise altitude, and aircraft weight. These can change, and therefore there are procedures in place to account for these changes. The addition of contingency fuel covers some of these changes, but a flight's OFP (operation flight plan) will often include a section detailing the change to fuel burn that comes from a weight change (1000 kg increase, for example) or a change in cruise altitude (for instance 2000 ft above or 2000 ft below the planned cruising level).

In particular for this question, the weight change could occur from last minute changes to the passenger load, or some extra fuel that the commander decides to take.

Any increase in aircraft weight increases the induced drag of the aircraft, thereby increasing the fuel burn. Any decrease in weight will therefore decrease the fuel burn.

Applying the reduction in the question, 1500 kg weight reduction is 1.5 x the 1000 kg reduction, so you can just multiply the 205 kg fuel reduction by 1.5 to get a total trip fuel that is 307.5 kg less than the original trip fuel requirement (closest answer 308 kg)