Last visit was: 24 Apr 2026, 02:46 It is currently 24 Apr 2026, 02:46
Home
Messages
Tests
Schools
Events
Close
GMAT Club Daily Prep
Thank you for using the timer - this advanced tool can estimate your performance and suggest more practice questions. We have subscribed you to Daily Prep Questions via email.

Customized
for You

we will pick new questions that match your level based on your Timer History

Track
Your Progress

every week, we’ll send you an estimated GMAT score based on your performance

Practice
Pays

we will pick new questions that match your level based on your Timer History
Not interested in getting valuable practice questions and articles delivered to your email? No problem, unsubscribe here.
Go to My Error Log Learn more
Close
Request Expert Reply
Confirm Cancel
Back to Forum
Create Topic
User avatar
Bunuel
User avatar
Math Expert
Joined: 02 Sep 2009
Last visit: 23 Apr 2026
Posts: 109,802
Own Kudos:
810,921
 [12]
Given Kudos: 105,868
Products:
GMAT Club Tests Forum Quiz
Expert
Expert reply
Active GMAT Club Expert! Tag them with @ followed by their username for a faster response.
Posts: 109,802
Kudos: 810,921
 [12]
A palindrome is a number that reads the same forward and backward. For 23 Jan 2020, 02:12
Kudos
Add Kudos
12
Bookmarks
Bookmark this Post
00:00
Start Timer
Pause Timer
Resume Timer
Show Answer
Hide
Show
History
B
Be sure to select an answer first to save it in the Error Log before revealing the correct answer (OA)!

Difficulty:

35% (medium)

Question Stats:

71% (01:23) correct 29% (01:29) wrong based on 248 sessions

History

Date
Time
Result
Not Attempted Yet
A palindrome is a number that reads the same forward and backward. For example - 1331. How many 4-digit palindromes can be formed using two of the five digits - 1, 3, 5, 7, and 9?

A. 10
B. 20
C. 30
D. 40
E. 60
ShowHide Answer
Official Answer
B
User avatar
GMATinsight
User avatar
Major Poster
Joined: 08 Jul 2010
Last visit: 24 Apr 2026
Posts: 6,976
Own Kudos:
16,912
 [3]
Given Kudos: 128
Status:GMAT/GRE Tutor l Admission Consultant l On-Demand Course creator
Location: India
GMAT: QUANT+DI EXPERT
Schools: IIM (A) ISB '24
GMAT 1: 750 Q51 V41
WE:Education (Education)
Products:
My Reviews
Expert
Expert reply
Schools: IIM (A) ISB '24
GMAT 1: 750 Q51 V41
Posts: 6,976
Kudos: 16,912
 [3]
A palindrome is a number that reads the same forward and backward. For 23 Jan 2020, 05:16
1
Kudos
Add Kudos
2
Bookmarks
Bookmark this Post
Bunuel
A palindrome is a number that reads the same forward and backward. For example - 1331. How many 4-digit palindromes can be formed using two of the five digits - 1, 3, 5, 7, and 9?

A. 10
B. 20
C. 30
D. 40
E. 60
Show more

FIve digits given: 1, 3, 5, 7, and 9

2 out of 5 digits can be chosen in 5C2 = 10 ways

Palindrome for any two chosen digits a and b can be made in two ways i.e. abba and baab

Total favourable outcomes = 5C2*2 = 10*2 = 20 ways

Answer: Option B
User avatar
CareerGeek
User avatar
Joined: 20 Jul 2017
Last visit: 23 Apr 2026
Posts: 1,286
Own Kudos:
4,432
 [2]
Given Kudos: 162
Location: India
Concentration: Entrepreneurship, Marketing
GMAT 1: 690 Q51 V30
WE:Education (Education)
GMAT 1: 690 Q51 V30
Posts: 1,286
Kudos: 4,432
 [2]
A palindrome is a number that reads the same forward and backward. For 23 Jan 2020, 05:24
Kudos
Add Kudos
2
Bookmarks
Bookmark this Post
Bunuel
A palindrome is a number that reads the same forward and backward. For example - 1331. How many 4-digit palindromes can be formed using two of the five digits - 1, 3, 5, 7, and 9?

A. 10
B. 20
C. 30
D. 40
E. 60
Show more

Let the 4 digit be ABCD
Number of options for A = 5
Number of options for B = 4 {Note that, 2 digits have to be used out of 5 available, A & B have to be different]
Number of options available for C & D = 1 each
--> Total number of selections possible = 5*4*1*1 = 20

Option B
User avatar
BhishmaNaidu99
User avatar
Joined: 22 Sep 2018
Last visit: 29 Jun 2020
Posts: 68
Own Kudos:
94
Given Kudos: 95
Schools: EDHEC MiM "22 (A)
Schools: EDHEC MiM "22 (A)
Posts: 68
Kudos: 94
A palindrome is a number that reads the same forward and backward. For 24 Jan 2020, 06:56
Kudos
Add Kudos
Bookmarks
Bookmark this Post
we can take 2 number from 5 numbers in 5c2 ways, each pair has again 2 possibilities, so 2*5c2 = 2*10 = 20 ways.
avatar
MT1302
avatar
Joined: 10 Jan 2023
Last visit: 05 Dec 2024
Posts: 94
Own Kudos:
846
Given Kudos: 36
Location: India
Posts: 94
Kudos: 846
A palindrome is a number that reads the same forward and backward. For 24 Dec 2023, 06:40
Kudos
Add Kudos
Bookmarks
Bookmark this Post
@
GMATinsight
Bunuel
A palindrome is a number that reads the same forward and backward. For example - 1331. How many 4-digit palindromes can be formed using two of the five digits - 1, 3, 5, 7, and 9?

A. 10
B. 20
C. 30
D. 40
E. 60

FIve digits given: 1, 3, 5, 7, and 9

2 out of 5 digits can be chosen in 5C2 = 10 ways

Palindrome for any two chosen digits a and b can be made in two ways i.e. abba and baab

Total favourable outcomes = 5C2*2 = 10*2 = 20 ways

Answer: Option B
Show more


Why are we not doing (5C2*2!)/(2!*2!) ? And when are we supposed to do (5C2*2!)/(2!*2!)(like what hint in the question suggests that we should do this ) ? Tell in case of digits or numbers also .
Bunuel or GMATinsight chetan2u
User avatar
chetan2u
User avatar
GMAT Expert
Joined: 02 Aug 2009
Last visit: 22 Apr 2026
Posts: 11,229
Own Kudos:
45,006
 [1]
Given Kudos: 335
Status:Math and DI Expert
Location: India
Concentration: Human Resources, General Management
GMAT Focus 1: 735 Q90 V89 DI81
Products:
My Reviews
Expert
Expert reply
GMAT Focus 1: 735 Q90 V89 DI81
Posts: 11,229
Kudos: 45,006
 [1]
A palindrome is a number that reads the same forward and backward. For 24 Dec 2023, 08:41
1
Kudos
Add Kudos
Bookmarks
Bookmark this Post
Gangadhar111990
@
GMATinsight
Bunuel
A palindrome is a number that reads the same forward and backward. For example - 1331. How many 4-digit palindromes can be formed using two of the five digits - 1, 3, 5, 7, and 9?

A. 10
B. 20
C. 30
D. 40
E. 60

FIve digits given: 1, 3, 5, 7, and 9

2 out of 5 digits can be chosen in 5C2 = 10 ways

Palindrome for any two chosen digits a and b can be made in two ways i.e. abba and baab

Total favourable outcomes = 5C2*2 = 10*2 = 20 ways

Answer: Option B


Why are we not doing (5C2*2!)/(2!*2!) ? And when are we supposed to do (5C2*2!)/(2!*2!)(like what hint in the question suggests that we should do this ) ? Tell in case of digits or numbers also .
Bunuel or GMATinsight chetan2u
Show more


If you are doing arrangements and there are repetition of a number.

In how many ways can you write numbers from 1, 3, 3, 1 ….. four numbers can be arranged in 4! ways but two are repeated so 4!/(2!2!)

But here we are initially finding combination by 5C2 and then arranging these 2 selected numbers in 2! ways. That is why 5C2*2!
User avatar
bumpbot
User avatar
Non-Human User
Joined: 09 Sep 2013
Last visit: 04 Jan 2021
Posts: 38,966
Own Kudos:
1,117
Posts: 38,966
Kudos: 1,117
A palindrome is a number that reads the same forward and backward. For 08 Nov 2025, 22:19
Kudos
Add Kudos
Bookmarks
Bookmark this Post
Automated notice from GMAT Club BumpBot:

A member just gave Kudos to this thread, showing it’s still useful. I’ve bumped it to the top so more people can benefit. Feel free to add your own questions or solutions.

This post was generated automatically.
Moderators:
Bunuel
Math Expert
109802 posts
Krunaal
Tuck School Moderator
853 posts