[Hints] 2013 Singapore MO (Junior Rd 1) Problem 26

2013 SMO (Junior-Rd1) 26. Given any 4-digit positive integer x not ending in ‘0’, we can reverse the digits to obtain another 4-digit integer y. For example if x is 1234 then y is 4321. How many possible 4-digit integers x are there if y - x = 3177?

Hint: Write x as x = \overline{abcd} = 1000a + 100b + 10c + 10d. What equation must a,b,c,d satisfy?

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