When to use a hint, undo or skip in a number puzzle
Learn when to use a hint, undo or skip in a number puzzle, and how to check rows, columns and boxes before spending sparks.
On a 6x6 board one column is almost complete. The most recent piece dropped a 4 into a space that should hold a 2. Above that 4 there are now four open cells. Before the next piece falls the player notices a problem in the third row. That row already contains a 4 farther along.
A player now faces three options. A hint reveals one correct number on the board. An undo reverses the most recent drop. A skip advances to another level. Every option requires sparks. Sparks are earned only by playing, never bought, so each use now leaves fewer for a hard board later.
Every level can be solved by logic alone, with no guessing. A stuck player can always go back to the rules: each row, column and box holds each number once. Numbers drop to the lowest empty cell, so the order of drops matters, and when a board stops moving, an earlier drop often needs another look. Checking row three, the column and the box for that 4 takes a few seconds and costs no sparks.
Check the rows, columns and boxes before a hint
Players who stall on a 6x6 board often begin with a single row. In the example above, that is row three: the player reads across all six cells and writes down which numbers from 1 to 6 are already there. Next comes the column the 4 fell into, read from top to bottom, and then the 2x3 box that holds the empty cell, which is two rows tall and three columns wide.
Many blocked cells open up once those three scans are done. Placed side by side, a row, column and box often rule out five of the six candidates for a cell that seemed open to any number.
Before they touch the tray, players mark the last remaining number in its cell. A few players tap the cell and keep the number in their head, while others say it aloud to a child seated nearby. Only after a second check against the other two groups does a player pick the number from the tray and tap the column.
The rules stay the same on every level, so this scan usually finds a cell with only one fitting number. Players rarely need a hint at this stage.
Undo a drop that broke a rule
A number that falls stays locked in its cell. One wrong drop, then, can cause trouble well beyond the cell it lands in. The example column has a 4 in a cell that needs a 2, and each later drop in that column lands on top of the mistake. Cells above are then filled in using a column that already holds a mistake. Several moves later, the player may see that no number fits at all.
Most players who catch the error do it right after the drop. Players look down the column and across the row they just changed, and the repeated number stands out while all four cells above are still empty. At that point undo takes back the 4 before another number falls, and the cell can be filled with the 2.
Undo costs a spark. A few players think one spark is a fair price for a single slip, since a wrong number on a 6x6 board can force a second and third wrong drop around it. Other players recheck the row, column and box before spending a spark, to confirm that the last drop alone broke a rule.
Skip a level and save sparks for hard boards
A skip suits a level where the scan has stalled. Every row, column and box has been read and the candidates for each empty cell listed, yet no cell has a single fitting number. Many players quit racing the timer after several minutes, since a rushed guess on a stalled board is not a move the rules allow. Once they spend a skip, they reach a fresh level and can think clearly again.
A skip does not change the star rules for the levels a player chooses to finish. The skipped level stays unfinished, but finishing fast with no mistakes on the other levels still earns 3 stars each.
Sparks are limited, so some players keep a few in reserve for a Master 9x9 level. That board gives more chances to stall, and one wrong drop early can reach many cells later. The same slip is usually easier to find and fix on a 4x4 or 6x6 board.
Sparks are never bought, only earned by playing, so a player can keep some for a Master 9x9 level and use undo first on a simple slip.
FAQ
What is the difference between a hint, an undo and a skip in a number puzzle?
A hint shows a correct number for one cell. An undo takes back the last drop and a skip moves the player on to a different level. Each of the three costs sparks, which players earn by playing.
Should I use undo if I put the wrong number in a cell?
Undo is most effective right after the wrong drop, while the cells above it remain empty. Before undoing, a player can check the row, column and box once more to confirm the last drop was the only one that broke a rule.
How do I find a number without using a hint on a 6x6 board?
Read the row, the column and the 2x3 box for the empty cell first, then list which numbers from 1 to 6 already appear in each group. If only one number fits the cell, check it against the other two groups before dropping it.
When is it worth skipping a level instead of stopping to think?
Skipping makes sense when every row, column and box has been read and no empty cell has only one fitting number. Players who keep sparks in reserve often save them for a larger 9x9 board.
Can every level be solved with logic and no guessing?
Every level can be solved by logic alone, so a stuck player can return to rule that each row, column and box holds each number once. When a board stops moving, an earlier drop often needs another look.
NumFall is made by the publisher of this site. Any health or brain-training points here are general information, not medical advice.