A car travels the first one third of a certain distance with a speed of 10 km/hr, the next one third distance with a speed of 20 km/hr and the last one third distance with a speed of 60 km/hr. thee average speed of the car for the whole journey is :
A. 18 km/hr
B. 24 km/hr
C. 30 km/hr
D. 36 km/hr
Answer: Option A
Solution(By Examveda Team)
Let the distance travelled by a car be x kmFirst $$\frac{x}{3}$$ km distance cover at speed of 10 km/hr
Second $$\frac{x}{3}$$ km distance cover at speed = 20 km/hr
Third $$\frac{x}{3}$$ km distance cover at speed = 60 km/hr
According to the question,
Total time ,
$$\eqalign{ & = \frac{x}{{3 \times 10}} + \frac{x}{{3 \times 20}} + \frac{x}{{3 \times 60}} \cr & = \frac{x}{{30}} + \frac{x}{{60}} + \frac{x}{{180}} \cr & = \frac{{6x + 3x + x}}{{180}} \cr & = \frac{{10x}}{{180}} \cr & = \frac{x}{{18}} \cr} $$
Average speed :
$$\eqalign{ & = \frac{{x \times 18}}{x}{\text{ km/hr}} \cr & = 18{\text{ km/hr}} \cr} $$
Related Questions on Speed Time and Distance
A. 48 min.
B. 60 min.
C. 42 min.
D. 62 min.
E. 66 min.
A. 262.4 km
B. 260 km
C. 283.33 km
D. 275 km
E. None of these
A. 4 hours
B. 4 hours 30 min.
C. 4 hours 45 min.
D. 5 hours
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