# Summation of hypergeometeric series

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.

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