Average Speed | Confusing

Expert replies

shekhar.kataria: Master | Next Rank: 500 Posts; Posts: 268; Joined: Mon Mar 15, 2010 12:10 am; Thanked: 13 times

by shekhar.kataria » Sat Jan 21, 2012 10:39 am

At 7:00am, Claire leaves the spa, driving her car at 80kph she reaches her house at 7:15am, packs her artwork, and at 7:45am, leaves for the design lab, which is 10km from her house. If she drives her car at 40kph in going to the design lab, what will her average speed be from the spa to the lab ?

O 30 kph
O 40 kph
O 53.3 kph
O 60 kph
O 66.7 kph

Source :- Gmatclub forums.
OA as per the poster :- A though i don't agree to this.

My Doubt :- Do we have to include half hour stop time to calculate average spped. If yes then the answer is correct.

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Source: Beat The GMAT — Problem Solving | Sat Jan 21, 2012 10:39 am

neelgandham: Community Manager; Posts: 1060; Joined: Fri May 13, 2011 6:46 amFollowed by: 52 members; Location: Utrecht, The Netherlands; Thanked: 318 times

by neelgandham » Sat Jan 21, 2012 11:10 am

Average speed of a trip = Total distance covered/Total time taken. So if you use the formula literally then I think the OA is correct. However, I, myself, am not sure if I can include the waiting time in theTotal time taken. We will wait for the experts to express their views on this.

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Brent@GMATPrepNow: GMAT Instructor; Posts: 16206; Joined: Mon Dec 08, 2008 6:26 pmFollowed by: 1268 members; Location: Vancouver, BC; Thanked: 5254 times; GMAT Score:770

by Brent@GMATPrepNow » Sat Jan 21, 2012 11:49 am

neelgandham wrote:Average speed of a trip = Total distance covered/Total time taken. So if you use the formula literally then I think the OA is correct. However, I, myself, am not sure if I can include the waiting time in theTotal time taken. We will wait for the experts to express their views on this.

If we're asked to find the average speed from spa to lab, we need to divide the total distance traveled by the total time elapsed. As such, we must include the 30 minutes when she is at home (during those 30 minutes, we can say that her speed is 0 kph)

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