The average speed of Gaurav during a two-way journey is 15 km/h. If he walked a distance of 20 km every hour while going, then his speed while returning will be:

Average speed for the entire journey = 15 km/h

Distance while going = Distance while returning = 20 km

Speed while going = 20 km/h

The formula for average speed over a round trip is:

​$$\text{Average Speed} = \frac{2 \times \text{Speed}_1 \times \text{Speed}_2}{\text{Speed}_1 + \text{Speed}_2}$$​​

where $$\text{Speed}_1$$​ is the speed while going, and $$\text{Speed}_2​$$​ is the speed while returning.

Substituting the given values into the average speed formula:

​$$15 = \frac{2 \times 20 \times \text{Speed}_2}{20 + \text{Speed}_2}$$​​

​$$15(20 + \text{Speed}_2) = 2 \times 20 \times \text{Speed}_2$$​​

​$$300 + 15 \times \text{Speed}_2 = 40 \times \text{Speed}_2$$​​

​$$300 = 40 \times \text{Speed}_2 - 15 \times \text{Speed}_2$$​​

​$$300 = 25 \times \text{Speed}_2$$​​

​$$\text{Speed}_2 = \frac{300}{25} = 12$$​​

Thus, The speed while returning is 12 km/h.