Question

A car covers $4$ successive $3$ km stretches at speeds of $10$ km/hr, $20$ km/hr, $30$ km/hr and $60$ km/hr respectively. The average speed of the car for the entire journey is

• A. $15$ km/hr
• B. $35$ km/hr
• C. $20$ km/hr
• D. $25$ km/hr

Answer 1

The correct option is C $20$ km/hr

$Averagespeed=\frac{totaldistance}{totaltime}$ and $time=\frac{distance}{speed}$

total distance = $4\times 3=12$

total time = $\frac{3}{10}+\frac{3}{20}+\frac{3}{30}+\frac{3}{60}=\frac{36}{60}$ hr

speed =$\frac{12}{36}\times 60=20$ kmph