ADDOKU-9 is more challenging. Each row and column contains the numbers 1 to 9, with no duplications.

Each row and column must add to 45. Look for starter cells, as explained above.

Put In trial pairs for sums of 3, 4, 16, and 17 because there is only one possible pair of numbers for each.

Note that there can be no 9s in sums under 9, no 1s in sums over 10, no 4s in a sum of 8 (because 4 can't be used twice), no 5s in a sum of 10, and so on.

ADDOKU is a free app of number puzzles. For a small fee, additional puzzles can be purchased from Apple’s App Store. The App collects no data regarding which users purchase the add-removal feature.

The App links to no websites, with the exception of  the App Store if you wish to buy more puzzles.  The user’s puzzle number is saved on the user's device within the App, but not transmitted anywhere.

Robert Smythe

In ADDOKU-7, place the numbers 1 to 7, with no duplications, in each row and column, so that the numbers add to the total in each pair or triplet of cells.

Since each row and column must add to 28, look for starter cells, a single cell that completes a row, column, or block. In this example, the three pairs down the first column add to 21. So the bottom left must be 7. It's in a pair that adds to 9, so its partner must be 2.

The pairs in the top two rows add to 60, so the cell that protrudes into row three must be 4. ( 60 - 2 x 28)  The rightmost 4 complete a 3-row block.

Look at column 2. A pair adding to 4 must be a 3 and 1, so those numbers are put in as trial numbers. A pair adding to 13 must be a 6 and 7. That leaves 4 and 5 in the pair adding to 9. But 4 is in use in the row, so solid numbers 5 and 4 can be entered.

During game, press to reveal correct and incorrect solid numbers.

Press to remove Incorrect solid numbers.

Press to display the possible choices for numbers in each cell. This changes as you add solid numbers and trial pairs.

Display the completed puzzle if you wish to stop before completing it.

Print the puzzle if you wish to do it on paper.

Switch to Trial to enter tentative numbers, shown in orange. Switch to Solid to enter numbers you have decided are correct.

From the top Menu, select this to add over a hundred new puzzles from the App Store.

On the Options page, you can change the display or set-up, or pick a specific Puzzle