Hi Aritra,

We have assumed that the entire journey takes T hour to complete. In that case, we have taken the distance as 40T.

Even when you take the distance as 50T, then the time taken while taking halt will be 5T/4, but the difference is simply not T/4 as we are calculating halt time per hour, which means we are calculating this difference over the total time taking halts. As in the previous scenario, our time including halt was T and the difference was T/5 more over this T.

Here , in this case, T/4 will be more over the total time taken while traveling with halts, i.e. 5T/4, and the question is asking us to calculate the time for which the bus stops per hour while taking halts, so for 5T/4 if it stops for T/4, for 1 hour it will be (T/4)/(5T/4), which is T/5.

Hope this helps.

Hi Viki,

Thanks for pointing out. We have updated the solution.

Hello Rick,
Here Total time travelled including the halts is T+x = 60+15 = 75 mins.
We have to find the halt time per hour travelled. 
Here 15 mins halt is for 75 mins.
So, find halt per hour. i.e $$\ \frac{\ 15}{75}\ \times\ 60$$ = 12 mins
Regards.

Thank you so much sir