STEP 4

START hunting down the identical twins. So in the 6th row down, the cage of 16 must contain 7/9 which means that cell with the twins 8/9 must contain an 8. Write that in and the accompanying 9 above it.

In the bottom-right block, use normal Sudoku rules with the number 5, and you find the cage of 14 must contain a 5/9, as 5 can’t go anywhere else. Equally in the cage of 8 which straddles the middleright and bottom-right blocks, a 5 has been placed, leaving 8-5=3 between the two remaining cells, so write in 1/2.

This means that above it where we have 1/7 in a cage of 8, that cell must contain the 7. Write in the 7 and the 1.