1-P method doesnt work.Please help

Expert replies

dddanny2006: Master | Next Rank: 500 Posts; Posts: 209; Joined: Thu Jan 12, 2012 12:59 pm

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

Like this post

Source: Beat The GMAT — Problem Solving | Mon Nov 25, 2013 11:14 am

GMAT/MBA Expert

[email protected]: Elite Legendary Member; Posts: 10392; Joined: Sun Jun 23, 2013 6:38 pmFollowed by: 511 members; Location: Palo Alto, CA; Thanked: 2867 times; GMAT Score:800

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]

Like this post

dddanny2006: Master | Next Rank: 500 Posts; Posts: 209; Joined: Thu Jan 12, 2012 12:59 pm

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

Like this post

Post new topic Post Reply

• Page 1 of 1

GMAT Course Reviews

559 reviews

1168 reviews

431 reviews

359 reviews

147 reviews

5/5

5 Star (560 Reviews)

"Target Test Prep is the closest to the official version of the GMAT exam, about 99% accuracy in terms of the quality and quantity of information. The course has excellently created singular sets of focused lessons and tests for every possible topic that one could come across in the official GMAT exam."

"The TTP course maximizes the efficiency of the time you spend studying. It will take time and effort but I could almost guarantee that if you complete the course exactly as it is laid out you will get an amazing score. They also have a very responsive team willing to help with any questions you might have."

"TTP has two things that I think no other test prep company offers: A teaching approach that reinforces understanding and an attitude that will give you the mental preparedness needed to succeed on the test. TTP gives you a deep understanding of the concept you need to know while teaching you how to think."

Write a Review