A motor car does a journey in 17.5 hours, covering the first half at 30 km/h and the second half at 40 km/h. Find the distance of the journey?

Answer: Option B

Let the total distance be 2X.

A_____X km_____M_____X km_____B

Total time taken in the journey = 17.5 hours
Time taken to cover X km at 30 km/h = $$\frac{\text{X}}{30}$$
Time taken to cover X km at 40 km/h = $$\frac{\text{X}}{40}$$
Now,
$$\begin{array}{rl}& \frac{X}{30}+\frac{X}{40}=17.5\\ & \frac{40X+30X}{1200}=17.5\\ & 70X=17.5\times 1200\\ & X=300km\\ & \text{Total}\text{distance},2x\\ & =600km\end{array}$$