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100 points for $49 worth of Veritas practice GMATs FREE VERITAS PRACTICE GMAT EXAMS Earn 10 Points Per Post Earn 10 Points Per Thanks Earn 10 Points Per Upvote ## Probability from GMAT prep ##### This topic has 4 expert replies and 1 member reply ## Probability from GMAT prep A basket contains 5 apples of which 1 is spolied & the rest are good. If henry is to select 2 apples from the basket simultaneously & at random, what is the probability that the 2 apples selected will include the spoiled apple. A. 1/5 B. 3/10 C. 2/5 D. 1/2 E 3/5 ### GMAT/MBA Expert GMAT Instructor Joined 25 May 2010 Posted: 15105 messages Followed by: 1859 members Upvotes: 13060 GMAT Score: 790 jkelk wrote: A basket contains 5 apples of which 1 is spolied & the rest are good. If henry is to select 2 apples from the basket simultaneously & at random, what is the probability that the 2 apples selected will include the spoiled apple. A. 1/5 B. 3/10 C. 2/5 D. 1/2 E 3/5 P(spoiled apple is selected) = 1 - P(spoiled apple is NOT selected). P(1st apple is not spoiled) = 4/5. (Of the 5 apples, 4 are not spoiled). P(2nd apple is not spoiled) = 3/4. (Of the 4 remaining apples, 3 are not spoiled). Since we want both events to happen, we multiply the fractions: 4/5 * 3/4 = 3/5. Thus, P(spoiled apple is selected) = 1 - 3/5 = 2/5. The correct answer is C. _________________ Mitch Hunt Private Tutor for the GMAT and GRE GMATGuruNY@gmail.com If you find one of my posts helpful, please take a moment to click on the "UPVOTE" icon. Available for tutoring in NYC and long-distance. For more information, please email me at GMATGuruNY@gmail.com. Student Review #1 Student Review #2 Student Review #3 Free GMAT Practice Test How can you improve your test score if you don't know your baseline score? Take a free online practice exam. Get started on achieving your dream score today! Sign up now. Legendary Member Joined 03 Apr 2011 Posted: 581 messages Followed by: 5 members Upvotes: 52 GMATGuruNY wrote: jkelk wrote: A basket contains 5 apples of which 1 is spolied & the rest are good. If henry is to select 2 apples from the basket simultaneously & at random, what is the probability that the 2 apples selected will include the spoiled apple. A. 1/5 B. 3/10 C. 2/5 D. 1/2 E 3/5 P(spoiled apple is selected) = 1 - P(spoiled apple is NOT selected). P(1st apple is not spoiled) = 4/5. (Of the 5 apples, 4 are not spoiled). P(2nd apple is not spoiled) = 3/4. (Of the 4 remaining apples, 3 are not spoiled). Since we want both events to happen, we multiply the fractions: 4/5 * 3/4 = 3/5. Thus, P(spoiled apple is selected) = 1 - 3/5 = 2/5. The correct answer is C. Hey Mitch, Whats the significance of the word "simultaneous" used here? doesnt it mean we cant calculate by picking one apple then other (please explain the part in bold) thanx ### GMAT/MBA Expert GMAT Instructor Joined 25 May 2010 Posted: 15105 messages Followed by: 1859 members Upvotes: 13060 GMAT Score: 790 killer1387 wrote: GMATGuruNY wrote: jkelk wrote: A basket contains 5 apples of which 1 is spolied & the rest are good. If henry is to select 2 apples from the basket simultaneously & at random, what is the probability that the 2 apples selected will include the spoiled apple. A. 1/5 B. 3/10 C. 2/5 D. 1/2 E 3/5 P(spoiled apple is selected) = 1 - P(spoiled apple is NOT selected). P(1st apple is not spoiled) = 4/5. (Of the 5 apples, 4 are not spoiled). P(2nd apple is not spoiled) = 3/4. (Of the 4 remaining apples, 3 are not spoiled). Since we want both events to happen, we multiply the fractions: 4/5 * 3/4 = 3/5. Thus, P(spoiled apple is selected) = 1 - 3/5 = 2/5. The correct answer is C. Hey Mitch, Whats the significance of the word "simultaneous" used here? doesnt it mean we cant calculate by picking one apple then other (please explain the part in bold) thanx The probability of picking the apples SIMULTANEOUSLY is no different from the probability of picking the apples WITHOUT REPLACEMENT. Both wordings convey the same restriction: each apple can be selected ONLY ONCE. Once an apple has been selected, it cannot be selected again. _________________ Mitch Hunt Private Tutor for the GMAT and GRE GMATGuruNY@gmail.com If you find one of my posts helpful, please take a moment to click on the "UPVOTE" icon. Available for tutoring in NYC and long-distance. For more information, please email me at GMATGuruNY@gmail.com. Student Review #1 Student Review #2 Student Review #3 Free GMAT Practice Test How can you improve your test score if you don't know your baseline score? Take a free online practice exam. Get started on achieving your dream score today! Sign up now. ### GMAT/MBA Expert GMAT Instructor Joined 08 Dec 2008 Posted: 12663 messages Followed by: 1246 members Upvotes: 5254 GMAT Score: 770 jkelk wrote: A basket contains 5 apples of which 1 is spolied & the rest are good. If henry is to select 2 apples from the basket simultaneously & at random, what is the probability that the 2 apples selected will include the spoiled apple. A. 1/5 B. 3/10 C. 2/5 D. 1/2 E 3/5 The two approaches shown above are the best (faster) approaches, but here's one more. Since there are so few objects involved (5 apples), we should be able to quickly answer the question by simply listing and counting Let A, B, C, D, and E represent the 5 apples, and let E represent the SPOILED APPLE We want to select 2 apples at random. So, let's list all of the possible outcomes: 1) AB 2) AC 3) AD 4) AE 5) BC 6) BD 7) BE 8) CD 9) CE 10) DE So, there are 10 possible outcomes Of those 10 possible outcomes, 4 outcomes include the SPOILED APPLE So, P(selection includes the spoiled apple) = 4/10 = 2/5 Answer: C Cheers, Brent _________________ Brent Hanneson – Creator of GMATPrepNow.com Use our video course along with Sign up for our free Question of the Day emails And check out all of our free resources GMAT Prep Now's comprehensive video course can be used in conjunction with Beat The GMAT’s FREE 60-Day Study Guide and reach your target score in 2 months! ### GMAT/MBA Expert GMAT Instructor Joined 09 Oct 2010 Posted: 1297 messages Followed by: 29 members Upvotes: 59 jkelk wrote: A basket contains 5 apples of which 1 is spoiled and the rest are good. If Henry is to select 2 apples from the basket simultaneously and at random, what is the probability that the 2 apples selected will include the spoiled apple? A. 1/5 B. 3/10 C. 2/5 D. 1/2 E 3/5 $5\,\,{\text{apples}}\,\,\left\{ \begin{gathered} \,1\,\,{\text{spoiled}} \hfill \\ \,4\,\,{\text{good}} \hfill \\ \end{gathered} \right.$ $? = P\left( {{\text{extract 2,}}\,\,{\text{1}}\,\,{\text{spoiled}}} \right)$ ${\text{total}}:\,\,C\left( {5,2} \right) = 10\,\,\,{\text{equiprobables}}$ ${\text{favorable:}}\,\,{\text{4}}\,\,\,\,\left( {{\text{spoiled}} + {\text{any}}\,\,{\text{good}}} \right)$ $? = \frac{4}{{10}} = \frac{2}{5}$ This solution follows the notations and rationale taught in the GMATH method. Regards, Fabio. _________________ Fabio Skilnik :: GMATH method creator ( Math for the GMAT) English-speakers :: https://www.gmath.net Portuguese-speakers :: https://www.gmath.com.br • FREE GMAT Exam Know how you'd score today for$0

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