Question

A bus maintains an average speed of $60$ km/hr while going from P to Q and maintains an average speed of $90$ km/hr while coming back from Q to P. The average speed of the bus is __________.

• A. $75$ km/hr
• B. $72$ km/hr
• C. $70$ km/hr
• D. $30$ km/hr

Answer 1

The correct option is B $72$ km/hr

Let the distance between P to Q be $x$

Time taken in going from P to Q $=\frac{x}{60}$

Time taken in going from Q to P $=\frac{x}{90}$

$\Rightarrow$ Average speed of bus $=$ Total Distance travelled $÷$ Total time taken $=\frac{2x}{\frac{x}{60}+\frac{x}{90}}=72$ km/hr