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Rohit

· started a discussion

· 1 Months ago

ROHIT (Question: 187965.0 )

If the distacnce is constant.we can find average speed with following approach.
AvgSpeed=2*x*y/(x+y)

here.. 2*30*20/(30+20)=24km/hr

Question:
A motor car goes from Mumbai to Pune at a speed of 20 km/hr but returns from there at a speed of 30 km/hr. The average speed of the car for the entire journey is –
Options:
A) 26 km/hr
B) 25 km/hr
C) 24 km/hr
D) 23 km/hr
Solution:
Ans: (c)


Alternate Sol:


Since,


Average speed = Total Distance / Total Time Taken


But we have only speeds S1 and S2


S1 = 20 km/hr


S2 = 30 km/hr


So now let us assume that the distance between a and b will be 60 km ( LCM of 20 and 30 )


D1 = 60 km


D2 = 60 km


Total Distance = D1 + D2 = 60 + 60 = 120 km


Now


T1 = D1/S1


T1 = 60/20 = 3 hr


T2 = D2/S2


T2 = 60/30 = 2 hr


Total Time = T1 + T2 = 3 + 2 = 5 hr


Now


Average Speed = Total Distance / Total Time = 120 / 5


Average Speed = 24 km/hr

Knowledge Expert

· commented

· 1 Months ago

Dear Student,

very Good.

Hope you have a great learning with us!!
All the Best,
Team Toprankers

NAMI

· commented

· 1 Months ago

thanks
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