The ratio of speeds of two trains is 7 : 8. If the second train covers 400 km in 4 hours, find the speed of the first train.

Given data

• Speed ratio (first : second) = 7 : 8
• Second train distance in 4 hours = 400 km ⇒ second train speed = 400 / 4 = 100 km/h

Concept / Approach

• In a ratio 7 : 8, let one part be k. Then first speed = 7k, second speed = 8k.
• Use the known second speed to find k.

Step-by-step calculation

Verification / Alternative

Common pitfalls

• Using 7/8 of the distance instead of the speed ratio.
• Forgetting to compute second speed first from the given 400 km in 4 h.

Final Answer