1. Examining the top three rows first Row two requires a 5. It has to be located in the middle 3x3 box. Two possible locations for 5 in centre box The centre column already has one 5 so it cannot be above the 8. Thus, it has to be above the 9 on the second row The number 5 appears in row one and row three.

2. Examining the top three rows first: 5 appears in row one and row three. Row two requires a 5. It has to be located in the middle 3x3 box. Two possible locations for 5 in centre box The centre column already has one 5 so it cannot be above the 8. Thus, it has to be above the 9 on the second row

3. Now scan down the three central columns :

4. The second and third columns already have the number 5 - but the first column also needs a 5. A 5 has to be located in the lower 3x3 grid box as the two above already have 5 in them. The bottom row of nine boxes has a 5 already so it cannot go in row 9. Thus, 5 has to go just above the 2 on the first row of the lower middle 3x3 grid box. Now scan down the three central columns :

5. Now examine the central three rows - row 4 to row 6. Fill in the number 2 in row 4 of the central 3x3 grid box. The number 2 appears in rows 5 and 6 but not in row 4 But Column 4 has a 2 already Thus, the 2 in row 4 has to go above the 4 in the central box

6. Now examine the central three rows - row 4 to row 6. Fill in the number 2 in row 4 of the central 3x3 grid box. The number 2 appears in rows 5 and 6 but not in row 4 But Column 4 has a 2 already Thus, the 2 in row 4 has to go above the 4 in the central box

7. Continue scanning across and down the columns and grids filling in the ‘easy’ numbers. It can help to systematically go through the numbers 1 to 9 in sequence for each horizontal and vertical group of three sub-grids.