A person travels from city A to city B at a speed of 50 kmph and returns from city B to city A at a speed of 40 kmph. If the total time taken for the journey is 9 hours, what is the distance between city A and city B ? 

Correct option is B

​Given:
1. Speed from city A to city B: 50 kmph
2. Speed from city B to city A: 40 kmph
3. Total time for the journey: 9 kmph
4. Let the distance between city A and city B be d km.

Formula Used:
1. Time for a journey:
Time = $$\frac{\text{Distance}}{\text{Speed}}$$​

2. Total time for the round trip:
$$\frac{d}{50} + \frac{d}{40} = 9$$​

Step-by-Step Solution:

Step 1: Set up the equation:

$$\frac{d}{50} + \frac{d}{40} = 9$$​

Take the LCM of 50 and 40, which is 200:

$$\frac{4d}{200} + \frac{5d}{200} = 9$$​

Simplify:
​$$\frac{9d}{200} = 9$$​​

Step 2: Solve for d :

$$d = \frac{9 \times 200}{9}$$​

d = 200 km​