relative speed

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vivek.kapoor83: Legendary Member; Posts: 833; Joined: Mon Aug 04, 2008 1:56 am; Thanked: 13 times

by vivek.kapoor83 » Wed Jan 07, 2009 1:21 am

im getting ans - 19.5 min......................as no option is there

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Source: Beat The GMAT — Problem Solving | Wed Jan 07, 2009 1:21 am

logitech: Legendary Member; Posts: 2134; Joined: Mon Oct 20, 2008 11:26 pmFollowed by: 25 members; Thanked: 237 times; GMAT Score:730

by logitech » Wed Jan 07, 2009 1:44 am

so the distance is (20-4)x5 = 16x5 ( there is no need to convert min to hr)

16x5=4xt

t=20 min

LGTCH
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"DON'T LET ANYONE STEAL YOUR DREAM!"

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vivek.kapoor83: Legendary Member; Posts: 833; Joined: Mon Aug 04, 2008 1:56 am; Thanked: 13 times

by vivek.kapoor83 » Wed Jan 07, 2009 1:55 am

relative speed -16 mph
Distance covered in 5 min - 1.3 miles
Now, at 4mph it will take -19.5 min to cover 1.3 mile...where i am gng wrong.pls correctme

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piyush_nitt: Master | Next Rank: 500 Posts; Posts: 424; Joined: Sun Dec 07, 2008 5:15 pm; Location: Sydney; Thanked: 12 times

by piyush_nitt » Wed Jan 07, 2009 2:10 am

vivek.kapoor83 wrote:relative speed -16 mph
Distance covered in 5 min - 1.3 miles
Now, at 4mph it will take -19.5 min to cover 1.3 mile...where i am gng wrong.pls correctme

Bold part equals to 1.333333333333333

thats the reason that your answer needs additional 30 seconds.

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logitech: Legendary Member; Posts: 2134; Joined: Mon Oct 20, 2008 11:26 pmFollowed by: 25 members; Thanked: 237 times; GMAT Score:730

by logitech » Wed Jan 07, 2009 2:11 am

vivek.kapoor83 wrote:relative speed -16 mph
Distance covered in 5 min - 1.3 miles
Now, at 4mph it will take -19.5 min to cover 1.3 mile...where i am gng wrong.pls correctme

Vivek this why you should not convery some X to Y ( miles/hr to miles/min) and convert it back!

Here is why you get 19.5:

16 miles 60 min

X miles 5 minutes

X = 16x5/60

X= 4/3

4/3 is 1.3333333333333333333333333333333333333 NOT 1.3

So if you use 4/3 instead of 1.3

4/3 = 4mph x TIME

TIME = 1/3 hr

1/3 hr is 20 minutes.

LGTCH
---------------------
"DON'T LET ANYONE STEAL YOUR DREAM!"

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vivek.kapoor83: Legendary Member; Posts: 833; Joined: Mon Aug 04, 2008 1:56 am; Thanked: 13 times

by vivek.kapoor83 » Wed Jan 07, 2009 2:43 am

hmmmm....strange...small mistake.......and wrong result............Thanks ligtech

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