Hello, phillipshwong!

This is classic problem . . .

. .

. .

. .

The surprising answer is: There areballs in the box at 12:00!no

At 1 minute before 12:00, we add balls #1 to #10 and remove one ball.

. . . . Suppose it is #1.

At minute to 12:00, we add #11 to #20 and remove one ball.

. . . . Suppose it is #2.

At minute to 12:00, we add #21 to #30 and remove one ball.

. . . . Suppose it is #3.

At minute to 12:00, we add #31 to #40 and remove one ball.

. . . . Suppose it is #4.

We continue this process until 12:00.

We can generalize the procedure:

At minute to 12:00, we add 10 balls and remove one ball.

. . . . Suppose it is number

At every fraction of a minute, we are adding 9 balls to the box.

Yet by 12:00, the box will be empty!

What about ball #35?

It was removed minute before 12:00.

What about ball #12,501

It was removed minute before 12:00.

Get it?