Helen

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okigbo: Master | Next Rank: 500 Posts; Posts: 177; Joined: Sun Aug 02, 2009 9:39 pm; Thanked: 6 times

by okigbo » Wed Oct 28, 2009 3:14 pm

How long did it take Helen to drive from home to her parents?
a. Helen's ave speed was 72Km/h
b. If Helen's ave speed had been 8km/h faster it would have taken her 1 hour less

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Source: Beat The GMAT — Data Sufficiency | Wed Oct 28, 2009 3:14 pm

venubab: Junior | Next Rank: 30 Posts; Posts: 13; Joined: Sun Nov 01, 2009 4:57 am; Thanked: 1 times

by venubab » Wed Nov 04, 2009 3:47 am

both statements are required

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getso: Master | Next Rank: 500 Posts; Posts: 141; Joined: Sat Feb 28, 2009 8:19 am; Thanked: 1 times

by getso » Wed Nov 04, 2009 5:45 am

Statement 1 tells only about average speed so its insufficient.

Statement 2 tells us if Helen's average speed had been 8km/h faster she would have saved 1 hour. Insufficient.

Let us take :
D- Distance from Home to her parents
S1-Initial Average speed i.e S1=72
T1-Time taken to reach travelling at speed of 72Km/hr

S2-If speed had been 8km/h faster then S2=72+8=80
T2-Time taken to reach travelling at speed of 80km/hr

Now applying speed formula, we know

T1=T2+1
D/S1=D/S2+1
D/72=D/80+1
Solving for D we get D=720

So T1=10 hours

Hence Helen takes 10 hours to reach her parents.

Hope this helps.

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