Summer is Coming! Join the Game of Timers Competition to Win Epic Prizes. Registration is Open. Game starts Mon July 1st.

 It is currently 22 Jul 2019, 16:00

### 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

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

# A palindrome is a number that reads the same forward and backward.

Author Message
TAGS:

### Hide Tags

Senior PS Moderator
Joined: 26 Feb 2016
Posts: 3356
Location: India
GPA: 3.12
A palindrome is a number that reads the same forward and backward.  [#permalink]

### Show Tags

31 Aug 2018, 10:58
1
1
00:00

Difficulty:

15% (low)

Question Stats:

80% (01:20) correct 20% (01:13) wrong based on 53 sessions

### HideShow timer Statistics

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

Source: Experts Global

_________________
You've got what it takes, but it will take everything you've got
Retired Moderator
Joined: 11 Aug 2016
Posts: 375
Re: A palindrome is a number that reads the same forward and backward.  [#permalink]

### Show Tags

31 Aug 2018, 11:09
1
pushpitkc wrote:
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

Source: Experts Global

How many 4-digit palindromes can be formed using two of the five digits - 1,3,5,7, and 9?

This means that the digits can not be repeated.

4 digit no looks like: _ _ _ _
We will start filling from the Thousands place.
Thousand's place can be filled in 5 ways.
Hundred's place can be filled in 4 ways.
Tenth's place has to be the same as hundreds place, so it can be filled in only 1 way.
One's Place has to be the same as hundreds place, so it can be filled in only 1 way.

Hence, 5x4x1x1= 20 ways.

_________________
~R.
If my post was of any help to you, You can thank me in the form of Kudos!!
Applying to ISB ? Check out the ISB Application Kit.
Director
Joined: 20 Feb 2015
Posts: 790
Concentration: Strategy, General Management
Re: A palindrome is a number that reads the same forward and backward.  [#permalink]

### Show Tags

01 Sep 2018, 00:08
1
pushpitkc wrote:
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

Source: Experts Global

No of ways we can select the first of the four digits = 5
no of ways we can select the next = 4
no of ways we can select the penultimate digit = 1 ( should be same as the previous)
no of ways we can select the last digit = 1 ( should be same as the first)

= 5*4*1*1=20

another way probably to look at it would be

no of ways we can select 2 out of 5 = 5c2 =10
no of ways the selected 2 can be arranged in the required way = 2(we have 2 ways to place the first one , remaining 3 places are placed in 1 way)
=10*2=20
VP
Joined: 09 Mar 2016
Posts: 1273
A palindrome is a number that reads the same forward and backward.  [#permalink]

### Show Tags

01 Sep 2018, 01:17
pushpitkc wrote:
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

Source: Experts Global

( 13, 15, 17, 19) * 2 = 8

(35, 37,39)*2 = 6

(57,59)*2 = 4

(7,9) *2 = 2

8+6+4+2 = 20

What a relieve when you understand how to solve the problem !!!!
Intern
Joined: 23 Oct 2013
Posts: 44
Re: A palindrome is a number that reads the same forward and backward.  [#permalink]

### Show Tags

01 Sep 2018, 03:57
if all four numbers are same such as 1111,5555

should we take this into accnt too
Director
Joined: 20 Feb 2015
Posts: 790
Concentration: Strategy, General Management
Re: A palindrome is a number that reads the same forward and backward.  [#permalink]

### Show Tags

01 Sep 2018, 04:01
sameeruce08 wrote:
if all four numbers are same such as 1111,5555

should we take this into accnt too

The question says 2 out of 5 , so we cannot take these into consideration.
Re: A palindrome is a number that reads the same forward and backward.   [#permalink] 01 Sep 2018, 04:01
Display posts from previous: Sort by