(i) If they run in the same direction.
(ii) If they run in the opposite direction.

correct answer is: c) 3.33 km & 30 km

Explanation

One bus speed is 40 km/hr
Another bus speed is 50 km/hr
Convert 20 minutes to hours = \frac{20}{60}\ hrs\ or\ \frac{1}{3}\ hrs
We know, Distance = Speed\ \times\ Time
\therefore Distance covered by one bus = \left(40\ \times\ \frac{1}{3}\right) km
\rightarrow\frac{40}{3} km.
And distance covered by another bus = \left(50\ \times\ \frac{1}{3}\right) km
\rightarrow\frac{50}{3} km
So that,
After 20 minutes distance between two buses in the same direction is
= \left(\frac{50}{3}\ -\ \frac{40}{3}\right) km
\rightarrow\frac{50\ -\ 40}{3} km
\rightarrow\frac{10}{3} km or 3.33 km.
After 20 minutes distance between two buses in the opposite direction is
= \left(\frac{50}{3}\ +\ \frac{40}{3}\right) km
\rightarrow\frac{50\ +\ 40}{3} km
\rightarrow\frac{90}{3} km or 30 km.
Ans: (i) Distance between two buses in the same direction is 3.33 km.
(ii) Distance between two buses in the opposite direction is 30 km.