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I have been trying this sudoku for nearly 5 hours now but im unable to find any number further...If anyone could help me out i would be really grateful.. enter image description here

Note: The numbers in black are the prefilled numbers. The numbers in blue are the ones i have found out. The numbers written in small and grey are the possible numbers that can go in that particular box(as i have found out...there may be a mistake in that :) )

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    $\begingroup$ Without giving away the complete solution: the 5 in the 3rd row must be either in the 7th or the 9th column. Whichever it is, we can exclude the 2nd row 7th column cell being a 5. The same logic can be used for other cells as well. $\endgroup$
    – elias
    Commented Jun 15, 2018 at 15:14
  • $\begingroup$ I put it through my own Sudoku solver, and it needed to make a guess at this point (though it did some more eliminations like @elias suggested). My solver handles "level 2" techniques, such as hidden/naked pairs and x-wing, but doesn't do "level 3" techniques such as triplets or swordfish. So this at least shows that it is a tricky one and that you haven't overlooked something simple. $\endgroup$
    – Jaap Scherphuis
    Commented Jun 15, 2018 at 15:26
  • $\begingroup$ Ahh yes thank you @elias and @ Jaap Scherphuis $\endgroup$
    – rohit_r
    Commented Jun 16, 2018 at 3:29
  • $\begingroup$ Maybe any of the advanced techniques in this answer (X-Wing, Swordfish, XY-Wing, Colouring, Remote Pairs, XY-Chain, Forcing Chains, etc.) helps to strike out some possible candidate-digits? $\endgroup$
    – Kevin Cruijssen
    Commented Jun 17, 2018 at 9:19

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In the 8th column, the 7 has to be in the middle box, so it can be removed from the 9th row.

The really hard thing to see is that if the element in the 9th row and 8th column is 2, then either you cannot have any 2 in the 1st column, or in the 4th row. Hence this element has to be 1.

After that, the Sudoku is easily solved.

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