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

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A palindrome is a number that reads the same forward and backward. For [#permalink] New post   24 Jan 2020, 07:20
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A palindrome is a number that reads the same forward and backward. For example - 1331. How many 4-digit palindromes can be formed using digits - 1, 3, 5, 7, and 9?

A. 10
B. 20
C. 25
D. 35
E. 45

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Re: A palindrome is a number that reads the same forward and backward. For [#permalink] New post   24 Jan 2020, 07:25
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5*5*1*1= 25.......??

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Re: A palindrome is a number that reads the same forward and backward. For [#permalink] New post   24 Jan 2020, 07:30
aish5063 wrote:
5*5*1*1= 25.......??

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Correct in my huble opinion, please post your approach...
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Re: A palindrome is a number that reads the same forward and backward. For [#permalink] New post   24 Jan 2020, 07:44
1st and 4th digit will be same... and 2nd and 3rd will be same.. so just choose 1st and 2nd digits.


repetition is allowed for 1st and 2nd spot
for 1st digit we have five options available.. and we have 5 options for second digit as well.
3rd and 4th will be same so...1,1 option for both spots...
that's why: 5*5*1*1

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A palindrome is a number that reads the same forward and backward. For [#permalink] New post   30 Mar 2020, 10:41
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repetition is allowed for 4th and 5th positions
for 1st digit we have five options available.. 1st and 5th will be same, hence 5th is 1
3rd and 4th will be same so...
so with different numbers we have 5*4*1*1 is 20
however we have to add -11111, 33333, 55555, 77777, 99999 as well. so 20+5 is 25
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Re: A palindrome is a number that reads the same forward and backward. For [#permalink] New post   30 Mar 2020, 11:17
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1st and 4th digit will be same.
2nd and 3rd digit will be same.
possibility for 1st number=5
possibility for 2nd number=5
Ans = 5*5=25
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Re: A palindrome is a number that reads the same forward and backward. For [#permalink] New post   27 Jun 2023, 03:35
Hello from the GMAT Club BumpBot!

Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos).

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Re: A palindrome is a number that reads the same forward and backward. For [#permalink]
27 Jun 2023, 03:35
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