Here's how to determine the number of atoms in the compound CaMg(CO3)2:

1. Identify the elements and their subscripts:

* Ca: Calcium - 1 atom

* Mg: Magnesium - 1 atom

* C: Carbon - 1 atom (multiplied by 2 from the subscript outside the parenthesis)

* O: Oxygen - 3 atoms (multiplied by 2 from the subscript outside the parenthesis)

2. Calculate the total number of atoms:

* Calcium: 1 atom

* Magnesium: 1 atom

* Carbon: 1 atom x 2 = 2 atoms

* Oxygen: 3 atoms x 2 = 6 atoms

3. Add the number of atoms for each element:

1 + 1 + 2 + 6 = 10 atoms

Therefore, there are 10 atoms in one molecule of CaMg(CO3)2.