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 →

combinatorics

Expert replies
Post new topic Post Reply
Previous Topic Next Topic
User avatar
Legendary Member
Posts: 659
Joined: Mon Dec 14, 2009 8:12 amFollowed by: 3 members
Thanked: 32 times
by Gurpinder » Sat Aug 07, 2010 6:50 am
If the first and last digit must be a 2 or a 4, how many 5-digit numbers are possible?


2*10*10*10*1 = 2000 (which is the wrong answer)

what am i doing wrong?
"Do not confuse motion and progress. A rocking horse keeps moving but does not make any progress."
- Alfred A. Montapert, Philosopher.
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: 1179
Joined: Sun Apr 11, 2010 9:07 pmFollowed by: 88 members
Location: Milpitas, CA
Thanked: 447 times

by Rahul@gurome » Sat Aug 07, 2010 6:57 am
Gurpinder wrote:If the first and last digit must be a 2 or a 4, how many 5-digit numbers are possible?


2*10*10*10*1 = 2000 (which is the wrong answer)

what am i doing wrong?
1st digit: 2 or 4; 2 ways
5th digit: 2 or 4; 2 ways
2nd digit: 0 to 9; 10 ways
3rd digit: 0 to 9; 10 ways
4th digit; 0 to 9; 10 ways

No. of 5 digit nos. that are possible = 2*2*10*10*10 = 4,000
Rahul Lakhani
Quant Expert
Gurome, Inc.
https://www.GuroMe.com
On MBA sabbatical (at ISB) for 2011-12 - will stay active as time permits
1-800-566-4043 (USA)
+91-99201 32411 (India)
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
User avatar
Legendary Member
Posts: 659
Joined: Mon Dec 14, 2009 8:12 amFollowed by: 3 members
Thanked: 32 times

by Gurpinder » Sat Aug 07, 2010 7:01 am
Rahul@gurome wrote:
Gurpinder wrote:If the first and last digit must be a 2 or a 4, how many 5-digit numbers are possible?


2*10*10*10*1 = 2000 (which is the wrong answer)

what am i doing wrong?
1st digit: 2 or 4; 2 ways
5th digit: 2 or 4; 2 ways
2nd digit: 0 to 9; 10 ways
3rd digit: 0 to 9; 10 ways
4th digit; 0 to 9; 10 ways

No. of 5 digit nos. that are possible = 2*2*10*10*10 = 4,000
Hey Rahul,

Thanks for the reply. But I have a question. I understand that the 1st digit has 2 options. But then wouldnt the last digit have 1 option left because 1 of those 2 options has already been selected for the 1st digit. so theres only one option left for the last one.?
"Do not confuse motion and progress. A rocking horse keeps moving but does not make any progress."
- Alfred A. Montapert, Philosopher.
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY

GMAT/MBA Expert

User avatar
GMAT Instructor
Posts: 1179
Joined: Sun Apr 11, 2010 9:07 pmFollowed by: 88 members
Location: Milpitas, CA
Thanked: 447 times

by Rahul@gurome » Sat Aug 07, 2010 7:25 am
Gurpinder wrote:
Hey Rahul,

Thanks for the reply. But I have a question. I understand that the 1st digit has 2 options. But then wouldnt the last digit have 1 option left because 1 of those 2 options has already been selected for the 1st digit. so theres only one option left for the last one.?
Gurpinder, it is not mentioned in the question that the digits 2 and 4 cannot be repeated, which means repetition of digits is allowed. Does that answer your query?
Rahul Lakhani
Quant Expert
Gurome, Inc.
https://www.GuroMe.com
On MBA sabbatical (at ISB) for 2011-12 - will stay active as time permits
1-800-566-4043 (USA)
+91-99201 32411 (India)
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
User avatar
Legendary Member
Posts: 659
Joined: Mon Dec 14, 2009 8:12 amFollowed by: 3 members
Thanked: 32 times

by Gurpinder » Sat Aug 07, 2010 7:28 am
Rahul@gurome wrote:
Gurpinder wrote:
Hey Rahul,

Thanks for the reply. But I have a question. I understand that the 1st digit has 2 options. But then wouldnt the last digit have 1 option left because 1 of those 2 options has already been selected for the 1st digit. so theres only one option left for the last one.?
Gurpinder, it is not mentioned in the question that the digits 2 and 4 cannot be repeated, which means repetition of digits is allowed. Does that answer your query?
Ahh... Thank you!
"Do not confuse motion and progress. A rocking horse keeps moving but does not make any progress."
- Alfred A. Montapert, Philosopher.
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY

GMAT/MBA Expert

User avatar
GMAT Instructor
Posts: 1179
Joined: Sun Apr 11, 2010 9:07 pmFollowed by: 88 members
Location: Milpitas, CA
Thanked: 447 times

by Rahul@gurome » Sat Aug 07, 2010 7:32 am
Gurpinder wrote:
Ahh... Thank you!
Welcome!
Rahul Lakhani
Quant Expert
Gurome, Inc.
https://www.GuroMe.com
On MBA sabbatical (at ISB) for 2011-12 - will stay active as time permits
1-800-566-4043 (USA)
+91-99201 32411 (India)
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Post new topic Post Reply
• Page 1 of 1