BREAKING: Target Test Prep releases Brand New 2026 On Demand GMAT prep course

Redeem
TTP OnDemand GMAT Video Course
Featured Course

Target Test Prep GMAT OnDemand

Scott Woodbury-Stewart’s private virtual classroom — 400 hours of master-class video lessons for the GMAT Focus Edition.

  • 715+ score guarantee — highest in the industry (99th percentile)
  • 52 chapters · 1,500+ lessons · 4,000+ practice questions
  • 400 hours of video · 1,500+ instructor-led HD smartboard lessons
  • 300,000+ students accepted to Harvard, Stanford, Wharton, Booth & Sloan & more
  • 24/7 live support + weekly Zoom office hours with GMAT instructors
  • TTP AI Assist — 24/7 AI-powered virtual tutor for instant help
  • 1,200+ flashcards + AI-powered study assistant & daily calendar
  • OnDemand, LiveTeach & GMAT Bootcamp formats available
  • Also: GRE, SAT Math & Executive Assessment courses
  • MBA Admissions Consulting now available
  • 🏆 2025 EdTech Breakthrough Award: Test Prep Solution Provider of the Year
  • 200,000+ students served
  • 5-day free trial — $0 to start, no auto-billing, cancel anytime
★★★★★ 5.0 (559 reviews)
130-pt guarantee
$0 to start then $127/mo
Start Free 5-Day Trial Read 559 Reviews →

White and black marbles - Please help

Expert replies
Post new topic Post Reply
Previous Topic Next Topic
Master | Next Rank: 500 Posts
Posts: 184
Joined: Tue Sep 07, 2010 9:43 amFollowed by: 1 member
Thanked: 6 times
by rahulvsd » Tue Mar 13, 2012 8:26 am
20 marbles were pulled out of a bag of only white marbles, painted black, and then put back in. Then, another 20 marbles were pulled out, of which 1 was black, afterwhich they were all returned to the bag. If the percentage of black marbles pulled out the second time represents their percentage in the bag, how many marbles in total does the bag currently hold?

Choices:
A 40
B 200
C 380
D 400
E 3200

[spoiler]OA: D. [/spoiler]
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Source: — Problem Solving |
Newbie | Next Rank: 10 Posts
Posts: 3
Joined: Wed Dec 14, 2011 9:44 am

by mbadreamsunlimited » Tue Mar 13, 2012 8:41 am
Ans : In second attempt 20 marbles pulled out. It contained 1 black marble. So % of black marble in second pull is 5%.

Since there are 20 black marble in back and the percentage of black marbles pulled out the second time represents their actual percentage in the bag.

Hence 20 = 5%of total marbles.
therefore total marbles = 400
Ans (D) 400
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
User avatar
GMAT Instructor
Posts: 509
Joined: Wed Apr 21, 2010 1:08 pmFollowed by: 85 members
Location: Irvine, CA
Thanked: 199 times
GMAT Score:750

by tpr-becky » Tue Mar 13, 2012 12:07 pm
from the first statement you know that you had 20 black marbles.

In the second statement 1/20 marbles were black and you are told that this is the same ratio as the black marbles in the bag - thus 1/20 marbles in the bag are black. you know that there are 20 black marbles so 1/20(marbles) = 20 thus marbles = 400 and D is the answer.
Becky
Master GMAT Instructor
The Princeton Review
Irvine, CA
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Post new topic Post Reply
• Page 1 of 1