A truck covers 640 km in 10 hours. A car covers the same distance in 8 hours. What is the ratio of the speed of the truck to the speed of the car?

Introduction / Context:
For equal distances, the speed is inversely proportional to time taken. Alternatively, compute speeds directly and take their ratio.

Given Data / Assumptions:
Distance = 640 km for both; Truck time = 10 h; Car time = 8 h.

Concept / Approach:
Compute speeds: v = distance/time. Then form the ratio truck : car.

Step-by-Step Solution:
Truck speed = 640 / 10 = 64 km/h. Car speed = 640 / 8 = 80 km/h. Ratio (truck : car) = 64 : 80 = 4 : 5.

Verification / Alternative check:
Using inverse proportionality: times 10 : 8 reduce to 5 : 4, so speeds are 4 : 5.

Why Other Options Are Wrong:
3 : 4, 1 : 2, 5 : 6 do not match the computed speeds.

Common Pitfalls:
Forgetting to simplify the ratio or mixing the order (car : truck instead of truck : car).

Final Answer:
4 : 5