Abdul while driving to school computes the average speed for his trip to be 20 km per hour on his return trip along the same route there is less traffic and average speed is 30 km per hour what is the average speed for Abdul strip
Answers
dist. while going = dist while returning
time = dist./speed
so, time while going = x/20
time while coming =x/30
total time= x/20+x/30
=(3x+2x)/60
=5x/60
=x/12
total dist.= 2x
avg. speed = total dist./total speed
=2x*12/x
=24km/hr
Answer:
Method I:
Let the distance traveled by Abdul from home to school = s km
time taken to reach the school=t1 sec
For Return journey , Abdul cover distance =s km
time=t2 sec
∴ Average speed for forward journey[home - school ] = Total distance/ Total time.
20 km/h =s/t1
∴t1=s/20 h ------eq(1)
Average speed for backward journey[school -home] = Total distance/ Total time.
30 km/h =s/t2
t2=s/30h -----eq(2)
Average distance for entire journey = Total distance/ Total time
=(s+s)/[s/20 +s/30]
=2s/s[1/20+1/30]
=2x20x30/50
=24 km/hr
Shortcut method : If equal distance are covered with speeds v1 and v2 then average distance=2v1v2/v1+v2
= 2x20x30/50
=24km/hr
∴ The average speed for Abdul's trip is 24km/h.
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Explanation: