Correct Answer - Option 4 : 720/43 km per hr

**Given **

Boy 1/3 distance walked at speed = 10 km per hr

Next 1/4 distance walked at speed = 20 km per hr

Rest distance walked at speed = 30 km per hr

**Here, the man covers not equal distance at different speeds.**

Let the distance be x km.

**∴ **Time is taken at 10 km per hr. distance one third (t_{1}) = x/(3×10) hrs

Time is taken at 20 km per hr. distance one-fourth (t_{2}) = x/(4×20)

Rest journey = x − (x/3 + x/4)

⇒ 5x/12

Rest journey time is taken at 30 km per hr. (t_{3}) = 5x/(12×30) hrs

Total time is taken in the whole journey = x/30 + x/80 + x/72

⇒ (24x + 9x + 10x)/720

⇒ 43x/720

**Average speed is** = (x)/43x/720

⇒ (720×x)/43x

**⇒ 720/43 km per hr**** **