Question

A car covers four successive $6km$ stretches at speeds of $25kmph$, $50kmph$, $75kmph$ and $150kmph$ respectively. Its average speed over this distance is:

• A. $25kmph$
• B. $50kmph$
• C. $75kmph$
• D. $150kmph$

Answer 1

The correct option is B $50kmph$

Average speed if distance is same $=4\times abcd/[abc+bcd+abd+acd]$ where a,b,c,d are the different speeds at same distance.

Now, according to the question,

Average speed $=4\times 25\times 50\times 75\times 150/\left[\right(25\times 50\times 75)+(50\times 75\times 150)+(25\times 50\times 150)+(25\times 75\times 150\left)\right]$

$=50$