Ramesh starts from a place J and reaches the place K in 28 hours. He travels 2/5 distance at the speed of 10 km/hr and the remaining distance at the speed of 20 km/hr. What is the distance between J and K?

Correct option is D

Given:
Time = 28 hours; Speed for 2/5 distance = 10 km/hr; Speed for 3/5 distance = 20 km/hr.
Formula Used:

$$\text{Total Distance} = \text{Distance}_1 + \text{Distance}_2 \\\text{Time} = \frac{\text{Distance}}{\text{Speed}}$$​

Solution:
Let total distance = D
​$$\text{Time for } \frac{2}{5} \text{ distance} = \frac{\frac{2}{5}D}{10} = \frac{D}{25} \\\text{Time for } \frac{3}{5} \text{ distance} = \frac{\frac{3}{5}D}{20} = \frac{3D}{100} \\\text{Total Time} = \frac{D}{25} + \frac{3D}{100} = \frac{4D}{100} = 28 \\D = 400 \, \text{km}$$​​
Answer: (d) 400 km