.
It is OBVIOUS, that there is a one-to-one correspondence between distinguishable arrangements of 14 balls in line
and in a 2 x 7 array.
So, the problem is EQUIVALENT to ask
"In how many distinguishable ways can 5 identical black balls
and 9 identical blue balls be arranged in a line ?"
The formula and the answer are
in = = 2002 ways.
Solved.
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On distinguishable permutations/arrangements, see the lesson
- Arranging elements of sets containing indistinguishable elements
in this site.