1. When the fourth person bought it, there were four eggs, and he bought four;

2. The third person bought eggs (4+ 1/2)×2=9.

3. The second person bought eggs (9- 1/2)×2= 17.

4. The first person bought eggs (17- 1/2)×2=33.

Comprehensive formula:

{[(4+ 1/2) * 2- 1/2] * 2- 1/2} * 2 = 33.

A: * * * There are 33 eggs.