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by Brent@GMATPrepNow » Mon Dec 07, 2015 8:46 am
rajan_agarwal wrote:Q. A travels 40 km at 8km/h and another 40km in 5hrs what is the average speed?
A travels 40 km at 8km/h
Distance = 40 km
Time = distance/speed = 40/8 = 5 hrs

A travel another 40km in 5hrs
Distance = 40 km
Time = 5 hrs


Average speed = (TOTAL distance)/(TOTAL time)
= (40 km + 40 km)/(5 hrs + 5 hrs)
= [spoiler]80/10 km/hr = 8 km/hr[/spoiler]
Last edited by Brent@GMATPrepNow on Sat Jan 02, 2016 5:17 pm, edited 1 time in total.
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by Amrabdelnaby » Sat Jan 02, 2016 2:44 pm
Hello Brent,

The second part of the question says another 40 km for 5 hours. 5 hours was the time not the speed; hence it yields to 8 kn per hour again. hence the average speed should be 8km/hr.

Right?
Brent@GMATPrepNow wrote:
rajan_agarwal wrote:Q. A travels 40 km at 8km/h and another 40km in 5hrs what is the average speed?
A travels 40 km at 8km/h
Distance = 40 km
Time = distance/speed = 40/8 = 5 hrs

A travel another 40km in 5hrs
Distance = 40 km
Time = distance/speed = 40/5 = 8 hrs


Average speed = (TOTAL distance)/(TOTAL time)
= (40 km + 40 km)/(5 hrs + 8 hrs)
= [spoiler]80/13 km/hr[/spoiler]
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GMAT/MBA Expert

User avatar
GMAT Instructor
Posts: 16207
Joined: Mon Dec 08, 2008 6:26 pm
Location: Vancouver, BC
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GMAT Score:770

by Brent@GMATPrepNow » Sat Jan 02, 2016 5:18 pm
Amrabdelnaby wrote:Hello Brent,

The second part of the question says another 40 km for 5 hours. 5 hours was the time not the speed; hence it yields to 8 kn per hour again. hence the average speed should be 8km/hr.

Right?
Brent@GMATPrepNow wrote:
rajan_agarwal wrote:Q. A travels 40 km at 8km/h and another 40km in 5hrs what is the average speed?
A travels 40 km at 8km/h
Distance = 40 km
Time = distance/speed = 40/8 = 5 hrs

A travel another 40km in 5hrs
Distance = 40 km
Time = distance/speed = 40/5 = 8 hrs


Average speed = (TOTAL distance)/(TOTAL time)
= (40 km + 40 km)/(5 hrs + 8 hrs)
= [spoiler]80/13 km/hr[/spoiler]
Good catch!
I edited my response accordingly.

Cheers,
Brent
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