Answer :
Given,
The time taken by Mr. john to cover 3/5 of the journey is 5 hours.
The distance covered by Mr, john in 3 hour is 200 km.
Consider,
The complete distance covered by the Mr john in the journey is x km.
According to the question,
[tex]\begin{gathered} x-\frac{3}{5}x=200km \\ 5x-3x=5\times200km \\ 2x=1000km \\ x=\frac{1000km}{2} \\ x=500km \end{gathered}[/tex]The total distance covered by the Mr. john in the journey is 500 km.
The distance covered by him in 3 hours is 200 km.
The distance covered by him in 5 hour is,
[tex]\frac{3}{5}x=\frac{3}{5}\times500=300km[/tex]The average speed of the whole journey is,
[tex]\begin{gathered} Average\text{ speed=}\frac{total\text{ distance}}{total\text{ time}} \\ =\frac{500}{5+3} \\ =\frac{500}{8} \\ =62.5km\text{ per hour} \end{gathered}[/tex]Hence, the average speed for the whole journey is 62.5 km per hour.