Question

Ram covers 20 kms at 6 kms per hr. and then further 42 kms at 9 kms per hr. Find his average speed for whole journey ?
1. 32/6 km per hr.
2. 42/5 km per hr.
3. 62/16 km per hr.
4. 31/4 km per hr.
5. 8/3 km per hr.

Answer 1

Correct Answer - Option 4 : 31/4 km per hr.

Given 

Ram covers 20 kms distance at = 6 km per hr

Next 42 km distance at = 9 km per hr 

Case I.

Distance = 20 kms

Speed = 6 Kms per hr.

∴ Time taken (t₁) = 20/6= 10/3 hrs.

Case II.

Distance = 42 kms

Speed = 9 km per hr.

∴ Time taken (t₂) = 42/9 hrs.

Total time = 10/3 + 14/3 = 24/3 = 8 hrs.

∴ Average speed = Todal Distance/Total time

⇒ 62/8 km per hr.

⇒ 31/4 km per hr