Please! Measure your palm with a ruler and see your last name.

If you don't tell him your last name is on that card, he can't tell it by measuring his palm.

This is just a math game.

His cards are numbered. Tell him your last name on those cards. He adds up the numbers of those cards to get a number, which corresponds to your last name. Each surname corresponds to a number (the card numbers with that surname are added up).

Give a simple example.

Such as Zhang, Wang and Li.

There is a card on the card 1, Wang; There are Wang and Li on card 2; There is one on number 3, Li;

You tell him that 1 2 exists, and 1+2=3 corresponds to the king;

You tell him that there are 2 and 3, 2+3=5 corresponding to Li;

You tell him that 1 3 is available, and 1+3=4 corresponds to one.

The principle of multiple surnames is the same, but it is more complicated.

Of course, your last name must be written on these cards. If you don't write, he can't say it.