Refer to figure.
(1) Calculate trip fuel. 
Ground Speed = 450 kt - 50 kt = 400 kt 
Distance DEP - DEST = 1000 NM 
Trip Time = 1000 NM / 400 kt = 2 h 30 min 
Fuel consumption = 2000 kg/h x 2 h 30 = 5000 kg

(2) Find out whether Aerodrome "A" is an En-route Alternate (ERA) or not. 
BASIC FUEL SCHEME WITH VARIATIONS — LOCATION OF THE FUEL EN ROUTE ALTERNATE AERODROME TO REDUCE CONTINGENCY FUEL TO 3 %

• The fuel en route alternate (fuel ERA) aerodrome should be located within a circle with a radius equal to 20 % of the total flight plan distance; the centre of this circle lies on the planned route at a distance from the destination aerodrome equal to 25 % of the total flight plan distance, or at least 20 % of the total flight plan distance plus 50 NM, whichever is greater. All distances should be calculated in still‑air conditions (see Figure 1). The fuel ERA aerodrome should be nominated in the operational flight plan.

1. "a circle having a radius equal to 20 % of the total flight plan distance" => 20% x 1000 = 200 NM​​​​​​ 
   the centre of which lies, at a distance of the destination aerodrome corresponding to: (greater of the 2 following calculations)
2. "25 % of the total flight plan distance" => 25 % x 1000 NM = 250 NM; OR
3. "at least 20 % of the total flight plan distance plus 50 NM" => 200 NM + 50 NM = 250 NM

Refer to the attached figure - we can conclude that alternate aerodrome A does not meet the requirements => the centre of the 200 NM radius circle is situated 750 NM from the departure aerodrome. According to the criteria, ERA A should be situated 750 - 200 = 550 NM from the departure aerdrome, and in reality it is situated 500 NM - Which means that contingency cannot be reduced to 3%.

(3) Calculate contingency according to regulation 
AMC1 CAT.OP.MPA.181 Fuel/energy scheme - fuel/energy planning and in-flight re-planning policy — aeroplane
BASIC FUEL SCHEME — PRE-FLIGHT CALCULATION OF USABLE FUEL FOR PERFORMANCE CLASS A AEROPLANES

…

(c) for contingency fuel, calculate for unforeseen factors either:

(1) 5 % of the planned trip fuel or, in the event of in-flight re-planning, 5 % of the trip fuel for the remainder of the flight; or

(2) an amount to fly for 5 minutes at holding speed at 1500 ft (450 m) above the destination aerodrome in standard conditions,

whichever is the higher;

BASIC FUEL SCHEME WITH VARIATIONS — CONTINGENCY FUEL 
(c) The contingency fuel should be the fuel described in points (c)(1) or (c)(2) of this AMC, whichever is higher:

(1) an amount of fuel that should be either:

(i) not less than 3 % of the planned trip fuel, or in the event of in-flight re-planning, 3 % of the trip fuel for the remainder of the flight provided that a fuel en route alternate (fuel ERA) aerodrome is available; or (This is NOT AVAILABLE in this case)
(ii) an amount of fuel sufficient for 20-minute flying time based upon the planned trip fuel consumption (this is NOT examined); or 
(iii) an amount of fuel based on a statistical fuel method that ensures an appropriate statistical coverage of the deviation from the planned to the actual trip fuel; prior to implementing a statistical fuel method, a continuous 2-year operation is required during which statistical contingency fuel (SCF) data is recorded — note: to use SCF on a particular city pair/aeroplane combination, sufficient data is required to be statistically significant; the operator should use this method to monitor the fuel consumption on each city pair/aeroplane combination, and to carry out a statistical analysis to calculate the required contingency fuel for that city pair/aeroplane combination; (this is NOT examined);

or

(2) an amount of fuel to fly for 5 minutes at holding speed at 1500 ft (450 m) above the destination aerodrome in standard conditions.

• (i)(A) = 5% x 5000 kg = 250 kg
• (ii) 5 min x 1200 kg/h = 100 kg
• The greater value is 250 kg