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Quote:
A man goes from home to office at an average speed of a km/hr. and on reaching office he realizes that he forgot his phone charger on his table at home. So, he immediately travels back to home at speed of b km/hr and reaches home. He maintained an average speed of c km/hr during his complete travel from home to office and then from office to home. is a≤10?
Understanding of the concept
Average speed formula is total distance/Total Time.
Also, Average speed is always closer to the slower speed.
Quote:
1) a ≤ b
No information about values of a and b, hence Insufficient
Quote:
2) c = 20 km/hr.
Lets understand and apply meaning of average speed, when a=10 and b=30, exact mid point is 20.
According to the question average speed is 20, as already mentioned average speed is closed to the slower speed, therefore a must be greater than 10. Sufficient
No calculation required, but only understanding of the concept.
B is correct.
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Let distance a to b be x
So total distance 2x
Time for atob x/a and b to a x/b
Total time x*a+b/ab
Avg speed of complete trip
2x*ab/x*(a+b) =c
2ab/a+b=c
#1 a<=b
Insufficient
#2 c =20
Or say
ab/a+b =10
Avg speed is 10
So a should a be >10
Option B


GMATinsight
A man goes from home to office at an average speed of a km/hr. and on reaching office he realizes that he forgot his phone charger on his table at home. So, he immediately travels back to home at speed of b km/hr and reaches home. He maintained an average speed of c km/hr during his complete travel from home to office and then from office to home. is a≤10?

1) a ≤ b
2) c = 20 km/hr.

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Archit3110
Let distance a to b be x
So total distance 2x
Time for atob x/a and b to a x/b
Total time x*a+b/ab
Avg speed of complete trip
2x*ab/x*(a+b) =c
2ab/a+b=c
#1 a<=b
Insufficient
#2 c =20
Or say
ab/a+b =10
Avg speed is 10
So a should a be >10
Option B



GMATinsight
A man goes from home to office at an average speed of a km/hr. and on reaching office he realizes that he forgot his phone charger on his table at home. So, he immediately travels back to home at speed of b km/hr and reaches home. He maintained an average speed of c km/hr during his complete travel from home to office and then from office to home. is a≤10?

1) a ≤ b
2) c = 20 km/hr.


How did you move forward from the highlighted part... Have you used GM >=HM ???
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QuantMadeEasy
Quote:
A man goes from home to office at an average speed of a km/hr. and on reaching office he realizes that he forgot his phone charger on his table at home. So, he immediately travels back to home at speed of b km/hr and reaches home. He maintained an average speed of c km/hr during his complete travel from home to office and then from office to home. is a≤10?
Understanding of the concept
Average speed formula is total distance/Total Time.
Also, Average speed is always closer to the slower speed.
Quote:
1) a ≤ b
No information about values of a and b, hence Insufficient
Quote:
2) c = 20 km/hr.
Lets understand and apply meaning of average speed, when a=10 and b=30, exact mid point is 20.
According to the question average speed is 20, as already mentioned average speed is closed to the slower speed, therefore a must be greater than 10. Sufficient
No calculation required, but only understanding of the concept.
B is correct.
How did you arrive at this . Nowehere it is mentioned that a > b or a < = b


Best !
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