I was solving a question on hypergeometric, I have been able to solve up to this part and need a simplification.
$ P(x_1)={_{13}}C_{x_1}/_{52}C_5\sum_{x_2 = 0}^{x_2=5} {_{13}}C_{x_2} \times _{26}C_{5-x_1-x_2} $ How do I simplifying this, I have tried to expand but I don't think its helping. NOTE: $C$ is the combination. A guideline to this will be appreciated.