$({\rm{Average\;speed\;}} = {\rm{\;}}\frac{{{\rm{\;Total\;distance}}}}{{{\rm{total\;speed}}}})$

Total distance travelled by Ajay

⇒ Distance covered in the first 3 hours + Distance covered in the next 5 hours

⇒ Distance covered in the first 3 hours = 3 x 60 = 180 km

⇒ Distance covered in the next 5 hours = 5 x 24 = 120 km

⇒ Total distance travelled = 180 + 120 = 300 km

⇒ Total time taken = 3 + 5 = 8 hours

$(\Rightarrow {\rm{\;Average\;Speed\;}} = {\rm{\;}}\frac{{300}}{8}\;{\rm{kmph}})$

⇒ Average speed = 37.5 kmph

∴ Average speed of Ajay's travel is 37.5 kmph