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# cancelling out

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CEO
Joined: 21 Jan 2007
Posts: 2760
Location: New York City
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Kudos [?]: 387 [0], given: 4

cancelling out [#permalink]  21 Apr 2007, 05:12
this is a probability question.

when a diver dives, there is a 20% chance of a perfect score. however, if a perfect score is given out, no one else will get a perfect score thereafter. janet is the third diver. what are her chances of receiving a perfect score?

8/10 x 8/10 x 2/10 = 128/1000, therefore 12.8%

my question is why cant we cancel out or simplify the fractions in this problem to make it 4/5x 4/5 x 1/5?
GMAT Instructor
Joined: 04 Jul 2006
Posts: 1266
Followers: 24

Kudos [?]: 167 [0], given: 0

We can indeed: 4/5 * 4/5 *1/5 =16/125 = 128/1000
GMAT Instructor
Joined: 04 Jul 2006
Posts: 1266
Followers: 24

Kudos [?]: 167 [0], given: 0

We can indeed: 4/5 * 4/5 *1/5 =16/125 = 128/1000
Manager
Joined: 28 Feb 2007
Posts: 197
Location: California
Followers: 2

Kudos [?]: 6 [0], given: 0

Re: cancelling out [#permalink]  22 Apr 2007, 11:55
bmwhype2 wrote:
this is a probability question.

when a diver dives, there is a 20% chance of a perfect score. however, if a perfect score is given out, no one else will get a perfect score thereafter. janet is the third diver. what are her chances of receiving a perfect score?

8/10 x 8/10 x 2/10 = 128/1000, therefore 12.8%

my question is why cant we cancel out or simplify the fractions in this problem to make it 4/5x 4/5 x 1/5?

I am not sure if I get you. You get the same answer either way
Manager
Joined: 02 Aug 2007
Posts: 232
Schools: Life
Followers: 3

Kudos [?]: 37 [0], given: 0

Re: cancelling out [#permalink]  14 Jun 2008, 12:10
bmwhype2 wrote:
this is a probability question.

when a diver dives, there is a 20% chance of a perfect score. however, if a perfect score is given out, no one else will get a perfect score thereafter. janet is the third diver. what are her chances of receiving a perfect score?

8/10 x 8/10 x 2/10 = 128/1000, therefore 12.8%

can someone tell me why we only do one outcome
Perfect, Not, Not

and not 2 outcomes
Perfect, Not, Not
Not, Not, Not

Shouldn't this be 2 outcomes that you add together?

Thanks,
Ali
Director
Joined: 14 Oct 2007
Posts: 758
Location: Oxford
Schools: Oxford'10
Followers: 13

Kudos [?]: 184 [0], given: 8

Re: cancelling out [#permalink]  14 Jun 2008, 12:15
h
x-ALI-x wrote:
bmwhype2 wrote:
this is a probability question.

when a diver dives, there is a 20% chance of a perfect score. however, if a perfect score is given out, no one else will get a perfect score thereafter. janet is the third diver. what are her chances of receiving a perfect score?

8/10 x 8/10 x 2/10 = 128/1000, therefore 12.8%

can someone tell me why we only do one outcome
Perfect, Not, Not

and not four outcomes
Perfect, Not, Not
Not, Perfect, Not
Not, Not, Perfect
Not, Not, Not

Thanks,
Ali

Ali,

here the only outcome is NOT, NOT , PERFECT (in that order) since once the Perfect happens it can't happen again and it says that Janet is the 3rd diver
CEO
Joined: 21 Jan 2007
Posts: 2760
Location: New York City
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Kudos [?]: 387 [0], given: 4

Re: [#permalink]  17 Jun 2008, 06:06
kevincan wrote:
We can indeed: 4/5 * 4/5 *1/5 =16/125 = 128/1000

yeaaaaaaaa im a dunce.
_________________

You tried your best and you failed miserably. The lesson is 'never try'. -Homer Simpson

Director
Joined: 14 Oct 2007
Posts: 758
Location: Oxford
Schools: Oxford'10
Followers: 13

Kudos [?]: 184 [0], given: 8

Re: Re: [#permalink]  17 Jun 2008, 07:55
bmwhype2 wrote:
kevincan wrote:
We can indeed: 4/5 * 4/5 *1/5 =16/125 = 128/1000

yeaaaaaaaa im a dunce.

that was well over a year ago

u been away bmw?
Re: Re:   [#permalink] 17 Jun 2008, 07:55
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