# Questions tagged [blackboard]

In a 'blackboard puzzle' a set of numbers is transformed according to certain rules.

19 questions
Filter by
Sorted by
Tagged with
499 views

### Variant of Abby and Bob and 3 numbers on the blackboard

Abby selects a positive integer $A$, and Bobby selects a positive integer $B$. They then both tell their number secretly to Summy. Summy writes the numbers $5$, $8$, and $15$ on the blackboard, and ...
3k views

### Abby and Bobby and three numbers on the blackboard

Abby selects a non-negative integer $A$, and Bobby selects a non-negative integer $B$. They then both tell their number secretly to Summy. Summy writes the numbers $5$, $8$, and $15$ on the ...
2k views

### The last number on the blackboard

The numbers 1, 2, ..., 500 are written on a blackboard. Each minute any two numbers are wiped out and their positive difference is written instead. At the end only one number remains. Which values can ...
164 views

### Replacing numbers on a board by their difference [duplicate]

The numbers from 1 to 1000 are written on a board. You are allowed to select any two numbers, erase them and write their difference on the board. If this process is repeated often enough, there is ...
569 views

### 99 numbers on the blackboard

The numbers 1,2,3, ..., 99 are written on the blackboard. Alice and Bob play the following game, taking turns. Alice starts. At every turn, each player removes one number until two numbers are ...
329 views

### Puzzle on a blackboard [closed]

What is the missing number in the picture above?(question is from some puzzle game) I tried some approaches, but haven't found any meaningful rule..thanks in advance!