Sudoku. Lesson 25 When all else fails. #2. The underlined pair.

well here we are the sudoko guy with our last lesson and it's another lesson called whenever you're stuck you've got nowhere to go here's another suggestion in other words similar to the last lesson but this time we say if that number doesn't work then the other number will providing everything else is correct but if you look at this puzzle in front of you boy well behind me actually if there's a lot of little numbers and that's what happens when you get to more difficult puzzles and here's a suggestion I have here a sheet and what I've done is printed out a sheet with large cells so that it's not quite as messy bearing in mind when some people do a puzzle like this they like to use a computer but if you don't use a computer you may want to go outside the puzzle and put all your numbers out in here that before you to work out what you go to put in here you can do that too or you can go by memory so you've got those choices now on today we're looking at an underlined pair now let me revise an underlined pair is usually a result of going outside the puzzle an underlined pair actually has only two numbers and you know that it's only those one of those two numbers that can go in that cell and that's why I put a line under them you probably notice me doing that quite a bit if you look at this puzzle we have several of them we have one here we have one there we have one down in here we have one there so there's you you usually get an underlined pair somewhere so the whole idea is if one number works then the other one doesn't or if one doesn't work the other one will and so again like you did in our last lesson we decide to choose a particular underlined pair that you think is going to get you somewhere well I've chosen for this puzzle this 4:8 now you can either be a four or it can be an eight we're going to try each of them and see what happens I'm going to start off with the four so I'm going to put a four in here and I'll use red so you can see what I'm doing we're we have four eight I'm going to put a 4 here and with that four what the ramifications well this becomes a 1 so we'll put a 1 in this becomes therefore you cancel this one and that becomes a 3 for matching pair if you've got a 1 here this becomes there's one there too so that becomes a 3 so we have to put in a 3 if that because that's a matching pair this has to become a 1 now then this block here because that is a 1 this will have to become a 6 and because that's a 6 if you go along the road there's another 6 here so it can't be a 6 there it becomes a 3 and this becomes a 1 well those we're getting somewhere somewhere so far we're getting there let's have a look at this block again where we started well because that eight is no longer there though it's only place you can put an 8 is there so I can do that and therefore the 7 has to go down here or it has to go down in here and that one will make this a 2 Wow we're making some progress here let's look at something else oh look here's this for that 4 means that this is going to be a 7 so we can rub that out that seven makes this a for that four makes this a seven now I just saw something down here see this three that makes this three of this three four of four now because that's the four this becomes a 3 because that's a 3 this becomes an 8 and this becomes a 3 but we've got trouble in River City this is a problem we can't go any further because guess what see this column here we have got two threes so using a four there doesn't work I'll be back in a second to redo this and show you what happens when you use an 8 there because remember we had a 4 & 8 there well here is the same puzzle same little numbers but this time using the 4 8 instead of using the 4 we're going to try with the number 8 and I'm going to use the red so you can see it easier as to what we've been doing and we'll start off with an 8 here that means we can get rid of the 4 8 it makes it less clutter II know it's a lot of people don't do that they just put a line through it or something like that it becomes a very messy page but if you like doing it that way that's fine but I'm going to rub them out today because it makes it easier for you to see on this board if that is 8 is gone that 8 is gone so this becomes a 7 if that becomes a 7 this no longer is a 7 therefore now what about a 4 here is a 4 and goes right along the bottom here so the 4 has to go there and that form means that we have 8 a 3 by 3 here it's a 1 2 and a 3 and the 1 2 and a 3 means that we know that a 1 2 & a 3 need not be over here in this line in this row so I can get rid of the 1 twos and threes over here so it's less fluttery we can rub that one out there's a 3 I can get rid of is another 3 I can get rid of there's another one I can get rid of because we know there's going to be a 1 2 and a 3 in there that's a little neat thing to keep an eye out for and this will be a 6 7 9 trip 3 by 3 as well well with that in mind let's see what we can do if I look at that 4 this becomes a 3 so we'll put the 3 in there if I look at that 3 this up here becomes an 8 that becomes an 8 therefore this becomes a 3 okay if that's the 3 this is no longer a 3 and this is no longer a 3 and this because of this 3 this is no longer a 3 and we're really getting somewhere now now this is interesting have a look at this folks this 3 here means that this has to be a 6 down here if that's the 6 we can get rid of the other sixes in this block so we're getting rid of all these little ones and when you get rid of them this way it's easier to see what's left now let's go on oh here's something here's a 7 here's a 7 over here so that means that this is a 4 is there a 4 down in here we can get rid of no help it here we can have a 7 so that becomes a 7 and this becomes a 4 and we've got that whole block done isn't that interesting so as there are four down here we can get rid of yes we can't use that for anymore so this becomes a 1 now that means we can get rid of this one and that's 4 and we can get rid of one this one and that 4 so this becomes an 8 if that's an 8 then this becomes a 7 oh boy we're really moving along here if that becomes a 7 this can be removed so we have a 4 9 there and because that's an 8 this is an 8 and that is a 4 9 - I just noticed something did you notice this and this is a way of checking well I've said a 49 and a 49 but have a look up here remember we did this in an earlier lesson we haven't a 4 9 on the right in that block we have we could have a 9 head down in here I think well we have to have an own if that's going to be a 9 and that's going to be 9 this is going to be a 9 so we can get rid of that 7 because we've got the 7 already up there so that becomes a 9 so now we have 4 9 on the right 4 9 on the left this has to be a 4 9 so to make it neat I would just simply redo it neatly so we can see them very easily and you don't have to have all those other little numbers in there for 9 for 9 remember we had a whole pile of little numbers in there we've eliminated them all we're down now to this pattern right left center using two numbers now let's push on this 7 here means that this has to be a 6 so we'll make it a 6 and I think that completes that column doesn't it fantastic and now we've only got one left in this block in it we've got a 6 and a 9 already so it has to be a 7 you know I did this a couple of days ago and sure enough every time you do it you'll find it you'll go different route and now I have this time too let's see what happens we've got a 4 9 then two four nine there we've only got three left in here well guess what we've got a three here a nine there so we don't need the nine anymore we can get rid of that one we can get rid of this nine and because of that situation here we've got a one-two three-one three-one two three we've got another three by three which is fair enough it's only what's left but I've just seen something else here because this is the six this becomes a 1 if that becomes a 1 that's in this block this becomes a 3 if that's the 3 then this becomes a 1 and here we go when the advantage of having a a 3 by 3 you can usually get or more because this 3 was with 1/3 that becomes a 1 therefore this becomes a 2 and this becomes a 3 and that's all because we you recognize that as the 3 by 3 and we recognize it this 6 made this a 1 which made out of 3 which made that 1 2 3 bang bang bang bang bang now because of that 3 I can get rid of this 3 and that's because of that too so we now have a 2 9 here now here we have we've got a 3 that we can get rid of this 3 well that's interesting by getting rid of that 3 we have a 1 2 and a 1 2 and a 1 3 this one means that this is going to be a 3 so we now left with a pair of one twos matching pair now it is interesting to note here that we've got a whole pile of numbers here and yet there's only one left or two left if I look at this number here 8 cancels that number out so that becomes a 9 didn't see that earlier will recur over it's still working out though that becomes a nine and this becomes an eight matching pair the value of a matching pair and that eight left center right works out and if that's the case the only number left in this whole column is a six if we count one two three four five six is missing so we know ones can go so we can put the six in there now let's see what the ramification of that is we have a top we have a middle this has to be a six so we can make that a six and therefore this becomes a 1 and if that becomes a 1 this has to come become a 2 that becomes a 2 and because that's a 2 this becomes a 1 I think think things are looking good now we know that yes that's right 1 so we have a top bottom middle and because of that - look at this this becomes a 9 that becomes a 9 and therefore this becomes a 2 and because this is a 2 and a 2 there I just want to give you a little clue if I do if you'd have gone ahead with the 4 and continued on you may have found that this 2 and this 2 are the same as it is this way and when you get that situation like this if you get 2 with doesn't matter with use the four or an eight though you know for sure that that is a 2 no doubt about it now let's there's a bit more to cover here let me see here we've got a 4 4 4 9 4 9 there's an 8 here that's interesting that means that this has to be a 4 if that's a 4 this becomes an 8 8 8:8 correct now because of that for down in here this becomes a nine because we're going to have two fours in the row and this becomes a four and I think we've done it let's have it stand back I'm looking so close that it sideways yeah we did it and it's so exciting when you try something like that little technique and it works out remember it's either one or the other number will work if all the numbers little numbers will correct so that's the end of the course I'd like to say a big thank you for those of you have taken the time to follow me all the way through this adventure and now it's only one thing I ask if you think it's gonna do you think it's worth it tell your friends so we're of one bye for now

Channel: Sudoku Guy

Views: 109,413

Keywords: how to solve sudoku, sudoku lessons, sudoku for all levels, sudoku for beginners, sudoku for dummies. how to solve sudoku puzzles, instructions on how to solve sudoku, demonstrations of sudoku solving. brain fitness, memory practise, sudoku for seniors, sudoku for the frustrated, advanced sudoku strategies, spare time activity, fun with sudoku, simple sudoku, solving sudoku tricks and hints, Brain fitness, sudoku solving strategies, sudoku, learn sudoku

Id: yDLgSgOuisI

Length: 16min 28sec (988 seconds)

Published: Wed Feb 11 2015