Question

Out of a total distance of $200$ km covered, first half is covered at the speed of $60$ km/hr and the remaining half is covered at $75$ km/hr . Find the average speed for the whole journey.

• A. $21\frac{2}{3}$ km/hr
• B. $66\frac{2}{3}$ km/hr
• C. $43\frac{2}{3}$km/hr
• D. $39\frac{2}{3}$ km/hr

Answer 1

The correct option is B $66\frac{2}{3}$ km/hr

Speed $=\frac{Distance}{Time}$
Average Speed $=\frac{TotalDistanceTravelled}{TotalTimeTaken}$

Since $100$ Km is covered at $60$ km/hr

Time, $t_1=\frac{Distance}{Speed}=\frac{100}{60}=\frac{5}{3}$ hr

And since another $100$ km is covered at $75$ km/hr

Time, $t_2=\frac{Distance}{Speed}=\frac{100}{75}=\frac{4}{3}$ hr

So, total time taken $=\frac{5}{3}+\frac{4}{3}=3$ hr.

Hence, average speed $=\frac{200}{3}=66\frac{2}{3}$ km/hr