28. Given a package containing 200 red marbles, 300 blue marbles and 400 green marbles. At each occasion, you are allowed to withdraw at most one red marble, at most two blue marbles and a total of at most five marbles out of the package. Find the minimal number of withdrawals required to withdraw all the marbles from the package.
28. Answer: 200 .

Since at most one red marble can be withdrawn each time, it requires at least 200 withdrawals.
On the other hand, 200 is possible. For example,
$$
150 \cdot(1,2,2)+20 \cdot(1,0,4)+10 \cdot(1,0,2)+20 \cdot(1,0,0)=(200,300,400) .
$$