Question

A boy covered one third of his journey at 20 km per hr. and the remaining two third at 40 km per hr. If the total journey is of 190 kms, what is the average speed for the whole journey?
1. 40 km per hr.
2. 20 km per hr.
3. 50 km per hr.
4. 30 km per hr.

Answer 1

Correct Answer - Option 4 : 30 km per hr.

Given

Total journey = 190 kms

Complete 1/3 journey at speed = 20 km per hr.

Reaming journey complete at = 40 km  pe hr

Calculation

1/3rd of journey = 190/3 km

Remaining 2/3rd of journey = (190 - 190/3) km

⇒ 380/ kms 

Time is taken in 1/3rd journey at 20km per hr (t₁) = (190)/3×20

⇒ 19/6 hr

Time is taken in 2/3rd journey at 40 km per hr. (t₂) = (380)3×40

⇒ 19/6 hr

Total time taken in whole journey = (t₁ + t₂) = (19/6) + (19/ 6)

⇒ 38/6  hr

Average speed = (190)/38/6 

⇒ 30 km per hr