Question

If a boy walks from his house to school at the rate of 4 km per hr, he reaches the school 10 minutes earlier than the scheduled time. However if he walks at the rate of 3 km per hr, he reaches 10 minuets late. Find the distance of his school from his house.
1. 4 kms.
2. 8 kms.
3. 6 kms.
4. 12 kms.

Answer 1

Correct Answer - Option 1 : 4 kms.

Given

 Boy speed 4 km per hr reached earlier at school = 10 minutes

 Boy speed 3 km per hr reached late at school = 10 minutes

Formula used:

Speed = Distance/Time

Calculation:

 Let the distance be x km.

Time is taken at 4 km per hr be t₁ =x/4 hrs 

Time taken at 3 km per hr be  t₂ =x/3 hrs 

Difference in timings = 10 + 10 

⇒ 20 minutes

According to the question

⇒ x/3 − x/4 = 20/60

⇒ x/12 = 1/3

 ⇒ x = 4 kms

∴ The required distance is 4 kms.