Question number 18. Andrew wants to complete the picture so that each row, column, and set of four circles connected by line segments contains the four numbers 1, 2, 3, and 4. What number should he write in the circle with the question mark? To start, I will say that if you are any way familiar with Sudoku, then you might know that sometimes you have to just put what values a circle could be in Sudoku Square, and then eventually the process will kind of eliminate some options and you might be able to end up with what the value actually is. So that's exactly what you have to do over here. So the first two entries of the first row are either 1, 4, 1, 4, or 4, 1, and that's because they're connected along this line segment over here to this 2 and 3. So of course only a 1 and a 4 is remaining. But what about the third entry in the first row? Well again, each column also has to have the same four numbers 1, 2, 3, and 4, so the third entry in this has to be either 3 or 4. But it also can't be 1 or 4 because they're in the same column. And that means that this entry has to be 3. So now we know that this is 1 or 4, this is 1 or 4, and this is 3. That means that the fourth entry in the first row has to be 2, so the answer is B. And again, just kind of keeping these up in the air but still having them be locked in as two possible numbers is really the key to solving this problem.

Sudoku

elimination

puzzle

grid

numbers