Question

Shilpa covered the distance at a speed of 20 km/h for 3 hours and the same distance at a speed of 15 km/h. Find the average speed (in km/h) of Shilpa.
1. 17 1⁄7  km/h
2. 15 1⁄2  km/h
3. 17 1⁄4  km/h
4. 15 1⁄4  km/h

Answer 1

Correct Answer - Option 1 : 17 1⁄7  km/h

Given:

Shilpa covers a distance at a speed of 20 km/h in 3 hours

The same distance is covered at a speed of 15 km/h

Formula used:

Distance = Speed × Time

Average speed = Total distance/Total time

Calculation:

According to the formula, we have

Distance = (20 × 3) km = 60 km

Here same distance has been covered twice

Time taken which covering same distance with 15 km/h = 60/15 hours 

⇒ 4 hours

And, Total distance  = (2 × 60) km = 120 km

Then, average speed = {120/(4 + 3)} km/h = (120/7) km/h

⇒ 17 1⁄7 km/h

∴ The required average speed is 17 1⁄7 km/h​.