A bus covers three successive 3 km stretches at speed of 10 km/hr, 20 km/hr and 60 km/hr respectively. Its average speed over this distance is :
A. 30 km/hr
B. 25 km/hr
C. 18 km/hr
D. 10 km/hr
Answer: Option C
Solution(By Examveda Team)
$$\eqalign{ & {\text{Average speed }} = \frac{{{\text{Total distance }}}}{{{\text{Total time}}}} \cr & {\text{Average speed}} = \frac{{60 \times 3}}{{\frac{{60}}{{10}} + \frac{{60}}{{20}} + \frac{{60}}{{60}}}} \cr & {\text{Average speed}} = \frac{{180{\text{ km}}}}{{\left( {6 + 3 + 1} \right){\text{ hr}}}} \cr & {\text{Average speed}} = \frac{{180{\text{ km}}}}{{{\text{10 hr}}}} \cr & {\text{Average speed}} = 18{\text{ km/hr}} \cr} $$
Short trick formula :
$$\left( {{\text{Average speed}} = \frac{{3xyz}}{{xy + yz + zx}}} \right)$$
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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