Question

A tractor plough along the sides of the square field of side 100 km long at a certain speed , if it increases its speed by 25% , it is able to finish the work 10 hours earlier . Find the actual speed of the tractor.

1. 10 km/hr
2. 8 km/hr
3. 20 km/hr
4. 15 km/hr
5. 6 km/hr

Answer 1

Correct Answer - Option 2 : 8 km/hr

Given:

Side of the field = 100 km

Calculations:

The total distance traveled = 4 × 100 = 400 km

Let the initial speed of the train = x km/hr

Actual time taken by the train =  400/x hrs

If it increases its speed by 25% , new speed will be ;

⇒ x + 25/100 x = x + x/4 = 5x/4

Time taken at increased speed = 400/(5x/4) = 1600/5x

According to question , 400/x – 1600/5x = 10     

⇒ 2000/5x – 1600/5x = 10

⇒  8 km/hr