I am struggling with the following question:Here is my working out:
Aircraft: 2109kg
Fuel 300 litres: 216kg
Flight fuel 110 litres: 79.2kg
Taxi fuel 3 gallons: 8.2kg

At take-off : Aircraft plus all fuel but less taxi
Take-Off: 2109+216-8.2 = 2316.8kg
Max Take-Off: 2950
Max weight to add: 2950-2316.8=633.2kg

At landing : Take-off less flight fuel
Landing : 2316.8-79.2 = 2237.6kg
Max Landing:2725
Max weight to add: 2725-2237.6=487kg

ZFW: 2109
Max Take-Off: 2950
Max weight to add: 2950-2109=521kg

In the suggested solution the answer is 480, which makes we wonder what I missed or where I wend wrong.

The old trap of not reading the question.

The 300 litres was where?

Try again and your answer might be more satisfying.

Thanks for taking a look. I accounted for 300 litres
Fuel 300 litres: 216kg

Unless I mixed something else up.

I accounted for 300 litres. Fuel 300 litres: 216kg

Indeed you did.

Unless I mixed something else up.

Not at all, that I can see.

But you still aren't reading the question ....

Question -

Fuel on board at take-off..........................300 litres

Your solution -

At take-off : Aircraft plus all fuel but less taxi

Right you are. Now I feel really silly.

Be relaxed. We all make mistakes.

Secret is to catch them and correct them before they cause any problems.

As you progress things get better and the error rate ramps down rapidly.