answer (Question: 187965.0 )

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KIRTI

· started a discussion

· 1 Months ago

answer (Question: 187965.0 )

sir how it come 60 km
it is not given in question

Knowledge Expert

· commented

· 1 Months ago

Its LCM of 20 and 30.

See comprehensive solution:

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

KIRTI

· started a discussion

· 1 Months ago

answer (Question: 187965.0 )

sir how it come 60 km
it is not given in question

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

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