A person can complete a journey in 10 hours. He covers the first one-third part of the journey at the rate of 28 km/h and the remaining distance at the rate of 84 km/h. What is the total distance of his journey?

Correct option is B

Given:
Total time = 10 hours
Speed for 1/3 distance (S1) = 28 km/h
Speed for 2/3 distance (S2) = 84 km/h
Formula Used:
Time = Distance / Speed
Solution:
Let total distance be x.
​$$\frac{x/3}{28} + \frac{2x/3}{84} = 10\\ \ \\\frac{x}{84} + \frac{2x}{252} = 10\\ \ \\\frac{3x + 2x}{252} = 10\\ \ \\5x = 2520 \Rightarrow x = 504 km$$​​
So the correct answer is (b).