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Palindrome

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Palindrome

by indiantiger » Mon May 31, 2010 9:52 am
SOURCE : MGMAT TEST

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

[spoiler]OA :C[/spoiler]

I got this wrong on the test. Would like to see a faster way to do it?
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by fibbonnaci » Mon May 31, 2010 10:58 am
A B C D these 4 letters represent the digits.

D can take up 5 values (1,3,5,7,9)
To fit the palindrome the first and last digit should be the same. so A can take up only 1 value (the value selected in D)

B can take up 10 values (0,1,2,3,4,5,6,7,8,9) and thus C can take up 1 value, the value selected in B.

so total is 5*10 => 50

Thus the number of 4 digit palindromes is 50

hope this helps!
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by indiantiger » Mon May 31, 2010 1:43 pm
Muchos gracias, I realized my mistake later on. I did not read the question properly and forgot the question is only asking for odd numbers.
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