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A palindrome is a number that reads the same forward and

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A palindrome is a number that reads the same forward and backward, suc [#permalink]

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A palindrome is a number that reads the same forward and backward, such as 121. How many odd, 4-digit numbers are palindromes?

A. 40
B. 45
C. 50
D. 90
E. 2500
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Re: A palindrome is a number that reads the same forward and backward, suc [#permalink]

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New post 26 Aug 2011, 09:47
enigma123 wrote:
A palindrome is a number that reads the same forward and backward, such as 121. How many odd, 4-digit numbers are palindromes?

a) 40
b) 45
c) 50
d) 90
e) 2500




First recognize you only need to consider the first two digits (because the second two are just the first two flipped)

There are 90 possibilities for the first two digits of a 4 digit number, 10-99 inclusive. Everything starting with a 1,3,5,7,9 will be odd, which is 5/9ths of the combinations.

5/9*90 = 50 C
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Re: A palindrome is a number that reads the same forward and backward, suc [#permalink]

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New post 31 Aug 2011, 10:47
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enigma123 wrote:
A palindrome is a number that reads the same forward and backward, such as 121. How many odd, 4-digit numbers are palindromes?

a) 40
b) 45
c) 50
d) 90
e) 2500


@enigma123: Here is my explanation:

A palindrome is a number that reads the same forward and backward. Examples of four digit palindromes are 1221, 4334, 2222 etc
You basically get to choose the first two digits and you repeat them in opposite order. Say, you choose 45 as your first two digits. The next two digits are 54 and the number is 4554.
Also, you need only odd palindromes. This means that you need an odd digit at the end i.e. 1/3/5/7/9. This means that you need to start the number with an odd digit. Only then will it end with an odd digit.

In how many ways can you pick two digits such that the first one is an odd digit?
The first digit can be selected in 5 ways.(1/3/5/7/9)
The second digit can be selected in 10 ways.(0/1/2/3...8/9)
Total = 5*10 = 50 ways
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Re: A palindrome is a number that reads the same forward and backward, suc [#permalink]

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New post 01 Sep 2011, 20:36
The question demands that in Palindrome, the first digit must be odd that is why the last digit becomes odd.
For example, 1221 is a palindrome that reads same backward and forward and it is odd.
So the easy way of solving it is;
Take first odd digit, there are five odd digit and five different ways of selecting it
The second digit can be both odd or even no restriction, therefore there are 10 different ways of selecting it

The first digit can be selected in 5 ways.(1/3/5/7/9)
The second digit can be selected in 10 ways.(0/1/2/3...8/9)
Total = 5*10 = 50 ways

The definite Answer is 50
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A palindrome is a number that reads the same forward and [#permalink]

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A palindrome is a number that reads the same forward and backward, such as 121. How many odd, 4-digit numbers are palindromes?

A. 40
B. 45
C. 50
D. 90
E. 2500
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Re: A palindrome is a number that reads the same forward and [#permalink]

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pratikbais wrote:
A palindrome is a number that reads the same forward and backward, such as 121. How many odd, 4-digit numbers are palindromes?

a) 40

b) 45

c) 50

d) 90

e) 2500


We want to determine how many odd 4-digit numbers like XYYX are there. Notice here that in a palindrome X and Y can be the same, for example 1111 or 3333 are also palindromes.

Since, the number must be odd then the first and the last digits (X's) can take 5 values (1, 3, 5, 7, or 9) and the two middle digits (Y's) can take 10 values (0, 1, ..., 9), so total such numbers possible is 5*10=50.

Answer: C.

Hope it's clear.
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Re: A palindrome is a number that reads the same forward and [#permalink]

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Re: A palindrome is a number that reads the same forward and backward, suc [#permalink]

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Re: A palindrome is a number that reads the same forward and backward, suc [#permalink]

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New post 06 Nov 2014, 05:59
Expert's post
enigma123 wrote:
A palindrome is a number that reads the same forward and backward, such as 121. How many odd, 4-digit numbers are palindromes?

A. 40
B. 45
C. 50
D. 90
E. 2500


Similar questions to practice:
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a-palindrome-number-reads-the-same-backward-and-forward-159265.html
a-palindrome-is-a-number-that-reads-the-same-forward-and-bac-161167.html

Hope it helps.
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Re: A palindrome is a number that reads the same forward and [#permalink]

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New post 03 May 2015, 11:20
HI Buneul,

A quick question with this problem. We can also make a palindrom out of event number also right.. such as 8228. Why does it have to be odd numbers.

Sorry a very old question.

pratikbais wrote:
A palindrome is a number that reads the same forward and backward, such as 121. How many odd, 4-digit numbers are palindromes?

A. 40
B. 45
C. 50
D. 90
E. 2500

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Re: A palindrome is a number that reads the same forward and [#permalink]

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New post 03 May 2015, 11:45
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shriramvelamuri wrote:
HI Buneul,

A quick question with this problem. We can also make a palindrom out of event number also right.. such as 8228. Why does it have to be odd numbers.

Sorry a very old question.

pratikbais wrote:
A palindrome is a number that reads the same forward and backward, such as 121. How many odd, 4-digit numbers are palindromes?

A. 40
B. 45
C. 50
D. 90
E. 2500


Because the question specifically asks about the number of odd palindromes.
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Re: A palindrome is a number that reads the same forward and [#permalink]

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New post 26 Oct 2015, 04:53
Bunuel wrote:
pratikbais wrote:
A palindrome is a number that reads the same forward and backward, such as 121. How many odd, 4-digit numbers are palindromes?

a) 40

b) 45

c) 50

d) 90

e) 2500


We want to determine how many odd 4-digit numbers like XYYX are there. Notice here that in a palindrome X and Y can be the same, for example 1111 or 3333 are also palindromes.

Since, the number must be odd then the first and the last digits (X's) can take 5 values (1, 3, 5, 7, or 9) and the two middle digits (Y's) can take 10 values (0, 1, ..., 9), so total such numbers possible is 5*10=50.

Answer: C.

Hope it's clear.


Hi Bunuel,

what about negative numbers? Shouldn't we multiply the result by 2 ?
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Re: A palindrome is a number that reads the same forward and backward, suc [#permalink]

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New post 28 Oct 2015, 18:19
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4 digits then the number must be in the format ABBA. A must be odd, so we have 5 possibilities for A. B can be whatever number, so it has 10 possibilities.
now, combine everything:
A = 5
B = 10
second B cannot be any of the 10 digits, it must be exactly as the first B, so it must be 1 combination
A = must be the same as first A, so there is only 1 combination
5*10*1*1 = 50
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Re: A palindrome is a number that reads the same forward and [#permalink]

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New post 17 Nov 2015, 19:17
Bunuel

Why is it not 2500? 5*10*10*5?
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Re: A palindrome is a number that reads the same forward and [#permalink]

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New post 17 Nov 2015, 22:17
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Hi dubyap,

Since the 4th digit has to match the 1st digit and the 3rd digit has to match the 2nd digit, you don't have as many options as you might think.

Since the palindrome has to be ODD, both the 1st and 4th digits have to be ODD and the SAME...

The 1st digit could be 1, 3, 5, 7 or 9
The 4th digit must MATCH the first digit, so once you choose the 1st digit, there is ONLY ONE possible number for the 4th digit.

The 2nd digit could be any of the 10 options (0 - 9, inclusive).
The 3rd digit must MATCH the 2nd digit, so once you choose the 2nd digit, there is ONLY ONE possible number for the 3rd digit.

Thus, there are...

(5)(10)(1)(1) = 50 options

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COMBINATIONS OF PALINDROMES [#permalink]

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New post 21 Mar 2016, 12:50
Q A palindrome is a number that reads the same forward and backward, such as 121. How many odd, 4-digit numbers are palindromes?

1. 40
2. 45
3. 50
4. 90
5. 2500

I HAVE THE ANSWER JUST NOT SATISFIED WITH THE EXPLANATION.

WOULD ANYONE PLEASE HELP ME IN GETTING THE PROBLEM..
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Re: A palindrome is a number that reads the same forward and backward, suc [#permalink]

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New post 21 Mar 2016, 13:00
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umg4147 wrote:
Q A palindrome is a number that reads the same forward and backward, such as 121. How many odd, 4-digit numbers are palindromes?

1. 40
2. 45
3. 50
4. 90
5. 2500

I HAVE THE ANSWER JUST NOT SATISFIED WITH THE EXPLANATION.

WOULD ANYONE PLEASE HELP ME IN GETTING THE PROBLEM..


Follow posting guidelines (link in my signatures), search for a question before starting a new thread, topic name should be the first few words of the question itself and add tags related to the question.

Topics merged.

Refer above for the solution.

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Re: A palindrome is a number that reads the same forward and backward, suc   [#permalink] 21 Mar 2016, 13:00
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