The average speed of a truck is one fifth of the speed of a bullet train.

The bullet train's speed is 2000 km ÷ 20 hours = 100 km/h. The truck's speed is one-fifth of this: 100 ÷ 5 = 20 km/h. In 54 minutes (0.9 hours), the truck covers 20 × 0.9 = 18 km.

Step-by-step Derivation:
Step 1: Calculate bullet train speed
Speed = Distance / Time = 2000 km / 20 h = 100 km/h

Step 2: Calculate truck speed
Truck speed = (1/5) × Bullet train speed = (1/5) × 100 = 20 km/h

Step 3: Convert 54 minutes to hours
54 minutes = 54/60 hours = 9/10 hours = 0.9 hours

Step 4: Calculate distance covered by truck
Distance = Speed × Time = 20 km/h × 0.9 h = 18 km