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 →

OG 13, Data Sufficiency Q71.

Expert replies
Post new topic Post Reply
Previous Topic Next Topic
Newbie | Next Rank: 10 Posts
Posts: 7
Joined: Tue Jan 24, 2012 8:29 am
Location: Mumbai, India
by vishrutsolanki » Tue Mar 19, 2013 6:21 am
Hey all !! I have a problem with the understanding of answer explanation of DS Q71 of OG 13.

The problem says that Mary persuaded n friends to donate 500$ and then each of these n friends persuaded n more people to donate 500$ each.

Now the answer explanation says that the total contribution made is $500(n^2+n).

Can some one explain how did the calculate the total contribution.
Vishrut Solanki

Before you achieve you must believe.
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Source: — Problem Solving |

GMAT/MBA Expert

User avatar
GMAT Instructor
Posts: 16207
Joined: Mon Dec 08, 2008 6:26 pmFollowed by: 1268 members
Location: Vancouver, BC
Thanked: 5254 times
GMAT Score:770

by Brent@GMATPrepNow » Tue Mar 19, 2013 6:27 am
vishrutsolanki wrote:Hey all !! I have a problem with the understanding of answer explanation of DS Q71 of OG 13.

The problem says that Mary persuaded n friends to donate 500$ and then each of these n friends persuaded n more people to donate 500$ each.

Now the answer explanation says that the total contribution made is $500(n^2+n).

Can some one explain how did the calculate the total contribution.
First round: n friends donate 500 dollars.
This gives us a total of 500n dollars in this round

Second round: n friends persuade n friends each to donate
So, each of the n friends gets n more people to donate.
The total number of donors in this round = n^2
This gives us a total of 500(n^2) dollars in this round

Total donations = 500n dollars + 500(n^2) dollars
We can rewrite this as 500(n + n^2) dollars
Or even 500n(1+n) dollars

Cheers,
Brent
Brent Hanneson - Creator of GMATPrepNow.com
Image
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Newbie | Next Rank: 10 Posts
Posts: 7
Joined: Tue Jan 24, 2012 8:29 am
Location: Mumbai, India

by vishrutsolanki » Tue Mar 19, 2013 6:41 am
Thank you Brent. That was simpler than i thought. Had spent at least 30 mins trying to figure out the expression. Thank you one more time.
Vishrut Solanki

Before you achieve you must believe.
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Post new topic Post Reply
• Page 1 of 1