Assertion (A): A boat takes longer to go a distance upstream and back on a flowing river than to cover the same total distance in still water.

Reason (R): The time lost going upstream is more than the time gained coming down.

Explanation

1. 01

   For a distance $d$: $\frac{d}{b - s} + \frac{d}{b + s} = \frac{2db}{b^{2} - s^{2}}$, which is more than $\frac{2d}{b}$ when $s > 0$. A is true.

2. 02

   R is why: the slow leg lasts longer, so it outweighs the fast one. Both are true and R explains A.