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Question :
A number is called a palindrome when it is equal to the number you get when all its digits are reversed. For example, 2772 is a palindrome. We discovered a curious thing. We took the number 461, reversed the digits, giving the number 164, and calculated the sum of these two numbers: 461 164 + ------- 625 We repeated the process of reversing the digits and calculating the sum two more times: 625 526 + ------- 1151 1511 + ------- 2662 To our surprise, the result 2662 was a palindrome. We decided to see if this was a pure coincidence or not. So we took another 3-digit number, reversed it, which gave a larger number, and added the two. The result was not a palindrome. We repeated the process, which resulted in another 3-digit number which was still not a palindrome. We had to repeat the process twice more to finally arrive at a 4-digit number which was a palindrome. What was the 3-digit number we started with the second time?
Category Logical & Aptitude Interview Questions
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Answers:

Because the reverse of the starting number is greater than the starting number itself, the first digit of the starting number must be less than the last digit. Therefore, the starting number must be at least 102. Secondly, we know that after two summations, the result has still only 3 digits.
abc
cba +
-------
def
fed +
-------
ghi
We know that def is not a palindrome. Therefore, d differs from f. This is only possible if d=f+1 (d can only be one greater than f, because b is at most 9). Since abc is at least 102, def is at least 403, so d+f will be at least 7. Since ghi is still a 3-digit number but not a palindrome, i can be at most 8, so d+f can be at most 8. Since d=f+1, d+f can only be 7, from which we conclude that a=1 and c=2. Now we have:
1b2
2b1 +
-------
4e3

To make the first digit of 4e3 a 4, b must be 5, 6, 7, 8, or 9. Now calculate the sum of 4e3 and 3e4:
4e3
3e4 +
-------
8h7
Because the first digit of the sum must be 8, e must be at least 5. Therefore, the only remaining candidates for b are 8 (8+8=16) and 9 (9+9=18). Now it can easily be found that b must be 9 and the starting number we are looking for is 192:
192
291 + (291 is greater than 192)
-------
483
384 +
-------
867 (still a 3-digit number)
768 +
-------
1635
5361 +
-------
6996 (the 4-digit palindrome).





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