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1-P method doesnt work.Please help

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1-P method doesnt work.Please help

by dddanny2006 » Mon Nov 25, 2013 11:14 am
If the probabilities are respectively 0.09,0.15,.21 and 0.23 that a person purchasing a new automobile will choose the color green,white,red or blue,what is the probability that a given buyer will purchase a new automobile that comes in one of those colors.

Answer 0.68---------------Simple method

Method 1


Prob(of choosing atleast one of those cars)=1-prob(of not choosing atleast one of those cars)

Prob(of not choosing atleast one of those cars)= 0.91*0.85*0.79*0.77=0.48

There 1-P=0.52

Why am I wrong here?
Answer is 0.68


Thanks

Dan
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by [email protected] » Mon Nov 25, 2013 3:09 pm
Hi dddanny2006,

In this question, we're told that the probability of choosing a car in a certain color is:

.09 = green
.15 = white
.21 = red
.23 = blue
.32 = some other color (this is implied, since total probability always adds up to 1)

We're asked for the probability of picking a car in ANY of those 4 colors (meaning green OR white OR red OR blue).

The probability formula = (What we want) / (Total possibilities)

Since we want "green or white or red or blue", we can simply add those up: .09 + .15 + .21 + .23 = .68

.68/1 = .68

The probability of NOT getting one of those colors is .32/1 = .32
So, 1 = .32 = .68

You can get the same answer with either approach, as long as you're doing the calculation that the question asks for.

GMAT assassins aren't born, they're made,
Rich
Contact Rich at [email protected]
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by dddanny2006 » Mon Nov 25, 2013 3:21 pm
What wrong did I do in the question,or in other words what should have been the question for the answer I got via my method

Thanks
[email protected] wrote:Hi dddanny2006,

In this question, we're told that the probability of choosing a car in a certain color is:

.09 = green
.15 = white
.21 = red
.23 = blue
.32 = some other color (this is implied, since total probability always adds up to 1)

We're asked for the probability of picking a car in ANY of those 4 colors (meaning green OR white OR red OR blue).

The probability formula = (What we want) / (Total possibilities)

Since we want "green or white or red or blue", we can simply add those up: .09 + .15 + .21 + .23 = .68

.68/1 = .68

The probability of NOT getting one of those colors is .32/1 = .32
So, 1 = .32 = .68

You can get the same answer with either approach, as long as you're doing the calculation that the question asks for.

GMAT assassins aren't born, they're made,
Rich
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