TRY IT · GUIDED EXAMPLE
Build the Hidden Triple
Small marbles show the colors left in the glowing row and in the center box. Find the three holes that share Teal, Yellow and Purple, strip their other notes, and watch a hidden single appear.
This is the real board from Marble Sudoku. The nine marble colors stand for the numbers 1 to 9.
- Find
- Strip
- Place
Build the Hidden Triple
Read the example in words
In row 6, Teal, Yellow and Purple fit only in columns 3, 4 and 5. Three colors, three holes: those holes must take them. So the other notes in those holes can go: Pink from column 3 and Navy from column 4. With Navy gone from row 6, column 4, Navy fits in only one hole of the center box: row 5, column 6. With numbers turned on, Teal is 4, Yellow is 6, Purple is 7, Pink is 3 and Navy is 8.
YOUR TURN · PRACTICE
Spot the Hidden Triples
Each round shows the small marbles in every hole. Tap the three holes of a hidden triple. On Easy the row, column or box glows and the three colors are named. On Hard you find them yourself.
Round color:
Why Hidden Triples work
Every row, column and box needs each number once. If three numbers can only go in three cells, each of those cells has to take one of them. No cell is left over for anything else.
That is why the other candidates in those three cells can’t be right, even when there are many of them. Removing them often uncovers a hidden single nearby, as in the example.
How to spot Hidden Triples faster
- Count where numbers fit. In one unit, find numbers with only two or three possible cells. Hidden triples are built from those.
- Match the cells. Look for three such numbers whose cells, put together, are just three cells.
- Don’t expect all three everywhere. A cell may hold only two of the three numbers. The pattern still works as long as the three cells are the only ones.
- Check the other side. In a unit with few empty cells, the rest often forms a naked group. Use whichever is easier to see.
Hidden Triples vs. Naked Triples vs. Hidden Pairs
| Hidden Triples | Naked Triples | Hidden Pairs | |
|---|---|---|---|
| What you look for | Three numbers that fit in only three cells | Three cells that hold only three numbers | Two numbers that fit in only two cells |
| Removes | Other candidates inside the three cells | Those numbers from the rest of the unit | Other candidates inside the two cells |
| Hard to see because | The cells are full of other candidates | The cells can show two of three numbers | The cells are full of other candidates |
| Difficulty | Intermediate | Intermediate | Intermediate |
Common mistakes
- A fourth cell. If one of the three numbers fits in a fourth cell of the unit, there is no hidden triple.
- Removing from other cells. A hidden triple only cleans its own three cells. The rest of the unit stays as it is.
- Mixing units. All three numbers must be counted in the same row, column or box.
- Expecting each cell to hold all three. A cell with two of the three numbers is fine. What matters is that no other cell takes them.
Hidden Triples FAQ
What is a hidden triple in Sudoku?
A hidden triple is three numbers that, in one row, column or box, can only go in the same three cells. Those cells must hold those numbers, so all other candidates in them can be removed.
What is the difference between hidden and naked triples?
A naked triple is three cells that contain only three numbers. A hidden triple is three numbers that appear only in three cells. Naked triples clear the rest of the unit, hidden triples clear the three cells themselves.
Does every cell need all three numbers?
No. Each cell needs at least one of them, and usually two. The rule is that no other cell in the unit can take any of the three.
Are hidden triples common?
They show up in harder puzzles, but they are easy to miss because the cells look busy. Counting where each number fits helps.
Does this work in Marble Sudoku?
Yes. In one row, column or box, look for three colors that fit only in the same three holes. Remove every other small marble from those holes.
When should I look for one?
After singles, pairs and naked triples stop finding moves. They are often what is left before X-Wings and other advanced patterns.
PRACTICE IN THE GAME
Find Hidden Triples in a real puzzle
When a puzzle stalls, count where each color fits in a busy row or box. Three colors sharing three holes clean up the board fast.
Next techniqueSwordfish
