Example 24. Take 3 numbers from $1,3,5,7,9$, and 2 numbers from $2,4,6,8$, to form a five-digit even number without repeated digits. How many such numbers can be formed?
There are $\mathrm{C}_{4}^{1} \cdot \mathrm{C}_{3}^{1} \cdot \mathrm{C}_{5}^{3} \cdot \mathrm{P}_{4}^{4}=2880($ ways).