Chapter 10 - Section 10.2 - Permutations and Combinations - 10.2 Assess Your Understanding - Page 695: 21

$C(26,13)=10,400,600$

Using the combination formula, we obtain: $C(n,r)=\frac{n!}{(n-r)!r!}$ $C26,13)=\frac{26!}{(26-13)!13!}=\frac{26!}{13!13!}=\frac{26\cdot25\cdot24\cdot23\cdot22\cdot21\cdot20\cdot19\cdot18\cdot17\cdot16\cdot15\cdot14\cdot13!}{13!\cdot13\cdot12\cdot11\cdot10\cdot9\cdot8\cdot7\cdot6\cdot5\cdot4\cdot3\cdot2\cdot1}=10,400,600$