Correct Answer - Option 1 :

\(34 \frac 2 7\) km/h

**Given:**

Distance traveled in one side = 120 km

Speed while going = 40 km/h

Speed while returning = 30 km/h

**Formula used:**

Average speed = Total distance travelled/Total time taken

**Calculation:**

Time taken while going = (120/40) hr

= 3 hrs

Time taken while returning = (120/30) hr

= 4 hr

Total distance travelled while going and returning = (120 × 2) km

= 240 km

∴ Average speed of the truck = (240/7) km/h

= \(34 \frac 2 7\) km/h