what is the average speed?

This topic has expert replies
Master | Next Rank: 500 Posts
Posts: 226
Joined: 09 Aug 2009

what is the average speed?

by ern5231 » Wed Aug 19, 2009 8:30 pm
Altogether walked from R to W for 12 hours. What is the average speed?
(1) First 8 hours were traveled at even speed of 56 mph
(2) Latter 8 hours traveled at avg speed of 56 mph

Legendary Member
Posts: 752
Joined: 17 May 2009
Location: Tokyo
Thanked: 81 times
GMAT Score:680

Re: what is the average speed?

by tohellandback » Wed Aug 19, 2009 9:37 pm
ern5231 wrote:Altogether walked from R to W for 12 hours. What is the average speed?
(1) First 8 hours were traveled at even speed of 56 mph
(2) Latter 8 hours traveled at avg speed of 56 mph
you missed something. plz correct the error and repost.
The powers of two are bloody impolite!!

User avatar
Master | Next Rank: 500 Posts
Posts: 157
Joined: 07 Oct 2008
Thanked: 3 times

by PussInBoots » Thu Aug 20, 2009 11:13 am
If even speed = constant speed, then the answer is (C)

From (A) we learn that first 4 hours the speed was 56mph, from (B) we learn that last 8 hours the avg. speed os 56mph. Hence 56mph is overall average speed.

Master | Next Rank: 500 Posts
Posts: 226
Joined: 09 Aug 2009

by ern5231 » Thu Aug 20, 2009 2:29 pm
Is this approach right? average speed = total distance / total time = 8 * 56 +8 * 56-4 * 56/12, choose c

Senior | Next Rank: 100 Posts
Posts: 36
Joined: 21 Jun 2009
Thanked: 1 times
GMAT Score:700

by iamjakekim » Thu Aug 20, 2009 5:26 pm
how did you solve this?

In a Q, it says 12 hours, but each statement gives 8 hrs, totaling 16 hrs.

I am confused

Master | Next Rank: 500 Posts
Posts: 164
Joined: 11 Jun 2008
Location: Bangalore
GMAT Score:590

by iwill » Thu Aug 20, 2009 11:07 pm
yeah.. if Even speed == constant speed Ans is C.

We need to find out the total distanve covered in 12 hrs.
From A : if he is traveling at a constant speed for 8 hrs, he covers 56*4 miles in first four hrs.
From B: if the average speed in the last 8 hrs is 56 mph, then Distance traveled in 8hrs = 56*8

Combining both, we can find the avg speed = (56*4+56*8)/12


~V