Digits in a circle
Discrete Mathematics
Level
2
Suppose we place \(K\) distinct digits around a circle such that each pair of adjacent digits (read either clockwise or counterclockwise) forms a number that's divisible by \(7.\) What's the maximum possible value of \(K?\)
For example, the diagram to the right illustrates a solution for \(K=3.\) Note that 35, 56, and 63 are all multiples of 7.
Note: Not all pairs of digits need to be read in the same direction. Some pairs may be read clockwise and others may be read counterclockwise.
by
An Phạm