Math Qn on White, Black and Red Marbles

This is posted by LL ☺

Qn on cbox: There are two containers A and B. Each of them contains 9 white marbles, 9 black marbles and 9 red marbles. If 10 marbles are removed from A and placed into B. how many marbles must be returned from B to A to make sure that there are at least 8 marbles of each colour in A?

Solution:
A: 9W, 9B, 9R
B: 9W, 9B, 9R

10 marbles are removed from A and placed into B. Assume 9W and 1B (any combination will do).
A: 0W, 8B, 9R
B: 18W, 10B, 9R

Now, return marbles from B to A to make sure that there are at least 8 marbles of each colour in A.
The most unlucky picks from B would be: 9R and 10B (A: 0W, 18B, 18R) followed by 8W (A: 8W, 18B, 18R)
Hence for worst case, number of marbles returned is 9+10+8 = 27 marbles.