Analysis: every two people hold it once, then everyone has to hold it three times; Four people shake hands 3 * * 4 times at a time, but this counts as shaking hands twice each time, so divide by 2.

Solution: solution: 3×4÷2

= 12÷2

=6 (times)

A: A * * * can shake hands six times.

Comments: This question belongs to the handshake problem. According to the calculation method of the total number of handshakes. The calculation method of the total number of handshakes is: number of handshakes = number of people × (number of people-1)÷2. Remember the formula of the number of handshakes and use it flexibly.

Extended data:

Matters needing attention in comprehensive calculation formula (four operations):

1. If there is only addition and subtraction or only multiplication and division, count from left to right.

2. If primary operation and secondary operation exist at the same time, the secondary operation is calculated first.

3. If there are primary, secondary and tertiary operations (i.e. power, root and logarithm operations) at the same time, first calculate the tertiary operation, and then calculate the other two levels.

4. If there are brackets, count the numbers in brackets first (no matter what level, count first).

5. The third level should be counted in brackets, and then the second and first levels should be counted.