Sudoku question

[Explorer-8]

I have come to a complete dead end on a sudoku. If I give you the wanted possible numbers in the first two columns only and in the first mini grid only, please tell me the PRINCIPLE of how to calculate which numbers to eliminate.

Column one: five empty squares:

148 - 178 - 678 - 67 - 46 - I can't form any triplets because whichever three groups I choose, there are always more than three different numbers when all the numbers from those groups are combined.

Column two: five empty squares:

78 - 47 - 5678 - 578 - 46 - It appears that 5678 can be one of a group of quadruplets, but only 578 and 78 will fit. I need one more group of numbers, but neither 47 nor 46 will fit.

Mini-grid one: four empty squares:

148 - 178 - 78 - 47 - If I could get a group of triplets from this, I could make a breakthrough, but I can't.

In some of the rows and columns, I have got pairs and triplets in, but no other spare empty squares to fit anything.

Is there a solution without resorting to trial and error? I can look up the answers at the back of the book, but that won't teach me anything.

[jan1956]

try http://www.sudokusolver.co.uk/

[Explorer-8]

Thanks, but the link didn't help in the way that I needed.

I have solved it now. I took just one of the mini grids which needed five squares to be filled and then I worked out how the answers in that mini grid were arrived at from the answers in the back of the book.

From 48 - 148 - 1378 - 378 - 47, I didn't realise that 48 - 148 is a pair because of the number 1, but yet it is.

That eliminates the number 4 from 47 leaving 7 in that square and then eliminating 7 from the other squares. It eliminates the number 8 from 1378 and from 378.

This leaves 48 - 148 - 13 - 3 - 7.

This becomes 48 - 48 - 1 - 3 - 7.

The rest of the sudoku was easy because all the other numbers fell into place, like a domino effect, by the same elimination process including eventually the 48 pair too.

[Explorer-8]

Thanks again, Jan1956.

This time, I looked again at sudokusolver.co.uk and I was able to find something to help me with an even harder sudoku, that is the Friday metroku. I used the step-by-step solution method and it helped me to learn some more principles of solving difficult sudokus such as pairs hidden within groups of numbers and how to eliminate a number that does not fit into a pattern rule.