MathDB

Given

3n

cards, each of them will be written with a number from the following sequence:

2, 3, ..., n, n + 1, n + 3, n + 4, ..., 2n + 1, 2n + 2, 2n + 4, ..., 3n + 3

with each number used exactly once. Then every card is arranged from left to right in random order. Determine the probability such that for every

i

with

1\le i \le 3n

, the number written on the

i

-th card, counted from the left, is greater than or equal to

i

Problem Statement