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That's the stage I'm now. I am looking at G block (one in left down corner) 4,5 value. I couldn't decide if it should be 4 or 5. How do I decide?

And, am I looking at the right place? Any alternate moves or suggestions?

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After singles, another very common sudoku pattern is known as the pointing pair. I've circled two squares that you've marked as only being 4 or 7. That means that they exclude other cells in the row and square from being 4 or 7. This lets you get a digit. You can try to apply this technique elsewhere as well.
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  • $\begingroup$ Correct me on this. 7,8 in E quadrant [(3,4,7,8),(3,7,8),(7,8)] is pointing pair. $\endgroup$ – Matheswaran Kanagarajan Jun 30 '18 at 2:33
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    $\begingroup$ That's unfortunately not a pointing pair, as there are three cells and two candidates. You need the number of cells to match the number of candidates (usually found when two cells in the same row/column/box have the same two possibilities remaining). (You could instead consider (3,4,7,8) to be a pointing quad in the 6th row, which would alternatively eliminate 4/7 in the center left box, but that's usually more work. $\endgroup$ – phenomist Jun 30 '18 at 2:40

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