Question

The ratio of the speeds of two trains is 3:4. If the second train covers 400 km in 5 hours, what is the speed of the first train?

• A. 60 km/h
• B. 80 km/h
• C. 90 km/h
• D. 120 km/h

Hint:

For ratio-based speed problems, calculate the known quantity first, then use the ratio to find the unknown.

Answer 1

The Correct Option is A

- Step 1: Speed of the second train = $\dfrac{400}{5} = 80$ km/h.
- Step 2: Let the speed of the first train be $S_1$ and the second be $S_2$. Given $S_1 : S_2 = 3 : 4$, and $S_2 = 80$ km/h.
- Step 3: Set up the ratio: $\dfrac{S_1}{80} = \dfrac{3}{4}$.
- Step 4: Solve for $S_1$: $S_1 = 80 \times \dfrac{3}{4} = 60$ km/h.
- Step 5: Verify: Ratio $60 : 80 = 3 : 4$, which holds.
- Step 6: Check options: Option (a) is 60 km/h, which matches.