At first, there were eight cards in each hand.

Take two from the left pile and put them in the middle pile. At this time, the left, middle and right are: 6 10 8 respectively.

Take another one from the right pile and put it in the middle pile. At this time, the left, middle and right are 6 1 1 7 respectively.

Finally, take a few cards from the middle pile and put them on the left, so that the number of cards on the left is twice that of the original. Namely:

The left side becomes 16, that is to say, the card of 10 is taken from the middle. At this time, the left, middle and right are 16 1 8 respectively.

There are 1 card left in the middle pile.

(2)

If each card starts with 12 cards.

Take two from the left pile and put them in the middle pile. At this time, the left, middle and right are 10 14 12 respectively.

Take another one from the right pile and put it in the middle pile. At this time, the left, middle and right are101511respectively.

Finally, take a few cards from the middle pile and put them on the left, so that the number of cards on the left is twice that of the original. Namely:

The left side becomes 24, which means taking 14 cards from the middle. At this time, the left, middle and right are 24 1 1 1 respectively.

There are 1 card left in the middle pile.

Can you understand this? :)