• Magoosh
Study with Magoosh GMAT prep

Available with Beat the GMAT members only code

• 5 Day FREE Trial
Study Smarter, Not Harder

Available with Beat the GMAT members only code

• Free Veritas GMAT Class
Experience Lesson 1 Live Free

Available with Beat the GMAT members only code

• Free Practice Test & Review
How would you score if you took the GMAT

Available with Beat the GMAT members only code

• Get 300+ Practice Questions
25 Video lessons and 6 Webinars for FREE

Available with Beat the GMAT members only code

• 5-Day Free Trial
5-day free, full-access trial TTP Quant

Available with Beat the GMAT members only code

• 1 Hour Free
BEAT THE GMAT EXCLUSIVE

Available with Beat the GMAT members only code

• Free Trial & Practice Exam
BEAT THE GMAT EXCLUSIVE

Available with Beat the GMAT members only code

• Award-winning private GMAT tutoring
Register now and save up to $200 Available with Beat the GMAT members only code ## There is a total of 120 marbles in a box, each of which is r tagged by: Brent@GMATPrepNow This topic has 3 expert replies and 3 member replies sachin_yadav Master | Next Rank: 500 Posts Joined 06 Dec 2010 Posted: 212 messages Followed by: 1 members Thanked: 5 times Target GMAT Score: 720 #### There is a total of 120 marbles in a box, each of which is r Wed Aug 06, 2014 3:10 am Elapsed Time: 00:00 • Lap #[LAPCOUNT] ([LAPTIME]) There is a total of 120 marbles in a box, each of which is red, green, blue, or white. If one marble is drawn from the box at random, the probability that it will be white is 1/4 and the probability that it will be green is 1/3. What is the probability that the marble will be either red or blue? (A) 1/6 (B) 1/4 (C) 2/7 (D) 1/3 (E) 5/12 OA E Please explain Regards Sachin _________________ Never surrender Need free GMAT or MBA advice from an expert? Register for Beat The GMAT now and post your question in these forums! ### GMAT/MBA Expert Brent@GMATPrepNow GMAT Instructor Joined 08 Dec 2008 Posted: 10860 messages Followed by: 1215 members Thanked: 5198 times GMAT Score: 770 Wed Aug 06, 2014 7:37 am sachin_yadav wrote: There is a total of 120 marbles in a box, each of which is red, green, blue, or white. If one marble is drawn from the box at random, the probability that it will be white is 1/4 and the probability that it will be green is 1/3. What is the probability that the marble will be either red or blue? (A) 1/6 (B) 1/4 (C) 2/7 (D) 1/3 (E) 5/12 ...the probability that it [the marble] will be white is 1/4 So, 1/4 of the 120 marbles are white. In other words, there are 30 white marbles. ...the probability that it [the marble] will be green is 1/3 So, 1/3 of the 120 marbles are green . In other words, there are 40 green marbles. Altogether, there are 70 marbles that are EITHER white or green. This means that the remaining 50 marbles are EITHER red or blue. So, P(selected marble is EITHER red or blue) = 50/120 = 5/12 Answer: E Cheers, Brent _________________ Brent Hanneson â€“ Founder of GMATPrepNow.com Use our video course along with Check out the online reviews of our course Come see all of our free resources Thanked by: sachin_yadav GMAT Prep Now's comprehensive video course can be used in conjunction with Beat The GMATâ€™s FREE 60-Day Study Guide and reach your target score in 2 months! ### GMAT/MBA Expert Brent@GMATPrepNow GMAT Instructor Joined 08 Dec 2008 Posted: 10860 messages Followed by: 1215 members Thanked: 5198 times GMAT Score: 770 Wed Aug 06, 2014 7:42 am sachin_yadav wrote: There is a total of 120 marbles in a box, each of which is red, green, blue, or white. If one marble is drawn from the box at random, the probability that it will be white is 1/4 and the probability that it will be green is 1/3. What is the probability that the marble will be either red or blue? (A) 1/6 (B) 1/4 (C) 2/7 (D) 1/3 (E) 5/12 Alternatively, we can use the COMPLEMENT. That is, P(Event A happening) = 1 - P(Event A not happening) So, P(selected marble is EITHER red or blue) = 1 - P(selected marble is NEITHER red nor blue) = 1 - P(selected marble is either white or green) = 1 - [P(marble is white) + P(marble is green)] = 1 - [1/4 + 1/3] = 1 - [3/12 + 4/12] = 1 - 7/12 = 5/12 Answer: E Cheers, Brent _________________ Brent Hanneson â€“ Founder of GMATPrepNow.com Use our video course along with Check out the online reviews of our course Come see all of our free resources GMAT Prep Now's comprehensive video course can be used in conjunction with Beat The GMATâ€™s FREE 60-Day Study Guide and reach your target score in 2 months! ### GMAT/MBA Expert GMATGuruNY GMAT Instructor Joined 25 May 2010 Posted: 13489 messages Followed by: 1790 members Thanked: 12985 times GMAT Score: 790 Wed Aug 06, 2014 12:02 pm sachin_yadav wrote: There is a total of 120 marbles in a box, each of which is red, green, blue, or white. If one marble is drawn from the box at random, the probability that it will be white is 1/4 and the probability that it will be green is 1/3. What is the probability that the marble will be either red or blue? (A) 1/6 (B) 1/4 (C) 2/7 (D) 1/3 (E) 5/12 Since the problem asks for a FRACTION, the total number of marbles can be ANY VALUE. Let the total number of marbles = the LCM of 3 and 4 = 12. If one marble is drawn from the box at random, the probability that it will be white is 1/4. Thus: W = (1/4)(12) = 3. If one marble is drawn from the box at random, the probability that it will be green is 1/3. Thus: G = (1/3)(12) = 4. Implication: Of the 12 marbles, the number that are R or B = 12-3-4 = 5. Since 5 of the 12 marbles are R or B, we get: P(R or B) = 5/12. The correct answer is E. _________________ Mitch Hunt GMAT Private Tutor GMATGuruNY@gmail.com If you find one of my posts helpful, please take a moment to click on the "Thank" icon. Available for tutoring in NYC and long-distance. For more information, please email me at GMATGuruNY@gmail.com. Thanked by: sachin_yadav 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. GMATinsight Legendary Member Joined 10 May 2014 Posted: 1000 messages Followed by: 21 members Thanked: 205 times Wed Aug 06, 2014 9:23 pm sachin_yadav wrote: There is a total of 120 marbles in a box, each of which is red, green, blue, or white. If one marble is drawn from the box at random, the probability that it will be white is 1/4 and the probability that it will be green is 1/3. What is the probability that the marble will be either red or blue? (A) 1/6 (B) 1/4 (C) 2/7 (D) 1/3 (E) 5/12 OA E Please explain Regards Sachin Total Probability = 1 i.e. 1 = Either White + or Green + or Red + or Blue i.e. 1 = (1/4) + (1/3) + (Probability of Red or Blue) i.e. (Probability of Red or Blue) = 1 - ((1/4)+(1/3) = 5/12 Answer: Option E _________________ Prosper!!! Bhoopendra Singh & Sushma Jha "GMATinsight" Contact Us Testimonials To register for One-on-One FREE ONLINE DEMO Class Call/e-mail e-mail: info@GMATinsight.com Mobile: +91-9999687183 / +91-9891333772 Get in touch for SKYPE-Based Interactive Private Tutoring One-On-One Classes fee - US$40 per hour &
for FULL COURSE (38 LIVE Sessions)-US\$1000

"Please click on 'Thank' if you like my post/response."

GMATinsight
Dwarka, New Delhi-110075 and Shivalik New Delhi

sachin_yadav Master | Next Rank: 500 Posts
Joined
06 Dec 2010
Posted:
212 messages
Followed by:
1 members
Thanked:
5 times
Target GMAT Score:
720
Sat Aug 09, 2014 6:28 am
Thank you for your replies. Appreciate it

Regards
Sachin

_________________
Never surrender

### GMAT/MBA Expert

Rich.C@EMPOWERgmat.com Elite Legendary Member
Joined
23 Jun 2013
Posted:
8820 messages
Followed by:
463 members
Thanked:
2815 times
GMAT Score:
800
Sat Aug 09, 2014 12:03 pm

Each of the methods outlined in this post can help you to get to the correct answer. Here's one more that is based on converting the data and using the structure of the answer choices to your advantage:

First off, in almost all cases, when the answers to a GMAT Quant question are numbers, they will be arranged from least to greatest. This will allow you to take advantage of approximation, rounding, etc., so that you can quickly eliminate answers that are "too big" or "too small"

In this prompt, we're dealing with some simple fractions (1/4 and 1/3), which you should be able to convert to decimal (you should have them memorized):

1/4 are white = .25 are white
1/3 are green = .33 are green (approximately)

.25 + .33 = .58 total of white and green (approximately)

The question asks for the probability of red or blue, so we haveâ€¦

1 - .58 = .42 total of red and blue (approximately)

The answers here are arranged from least (1/6 = .1666) to greatest (5/12 = let's not mess with this just yet)

Answer D = 1/3 = .33, which is TOO LOW (we're looking for approximately .42). This means that A, B and C are also TOO LOW.

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

_________________
Contact Rich at Rich.C@empowergmat.com

### Best Conversation Starters

1 LUANDATO 157 topics
2 lheiannie07 87 topics
3 Roland2rule 75 topics
4 ardz24 64 topics
5 AAPL 58 topics
See More Top Beat The GMAT Members...

### Most Active Experts

1 EconomistGMATTutor

The Economist GMAT Tutor

163 posts
2 GMATGuruNY

The Princeton Review Teacher

133 posts
3 Jay@ManhattanReview

Manhattan Review

128 posts
4 Rich.C@EMPOWERgma...

EMPOWERgmat

121 posts
5 Brent@GMATPrepNow

GMAT Prep Now Teacher

100 posts
See More Top Beat The GMAT Experts