Respuesta :
Hello! First, let's write some important information contained in the exercise:
committee = 6 students
class: 28 students:
- 10 males
- 18 females
Let's consider the rule: At least three females must be on the committee, so we have some cases, look:
_F_ * _F_ * _F_ * __ * __ * __
1st option:
3 females and 3 males
_F_ * _F_ * _F_ * _M_ * _M_ * _M_
2nd option:
4 females and 2 males
_F_ * _F_ * _F_ * _F_ * _M_ * _M_
3rd option:
5 females and 1 male
_F_ * _F_ * _F_ * _F_ * _F_ * _M_
4th option:
6 females and 0 male
_F_ * _F_ * _F_ * _F_ * _F_ * _F_
Now, we have to use the formula below and find the number of possible combinations:
[tex]C_{n,p}=\frac{n!}{p!\cdot(n-p)!}[/tex]Let's calculate each option below:
1st:
3 females:
[tex]C_{18,3}=\frac{18!}{3!\cdot(18-3)!}=\frac{18\cdot17\cdot16\cdot15!}{3\cdot2\cdot1\cdot15!}=\frac{4896}{6}=816[/tex]3 males:
[tex]C_{10,3}=\frac{10!}{3!\cdot(10-3)!}=\frac{10\cdot9\cdot8\cdot7!}{3\cdot2\cdot1\cdot7!}=\frac{720}{6}=120[/tex]3 females and 3 males: 816 * 120 = 97920
2nd option:
4 females:
[tex]C_{18,4}=\frac{18!}{4!\cdot(18-4)!}=\frac{18\cdot17\cdot16\cdot15\cdot14!}{4\cdot3\cdot2\cdot1\cdot14!}=\frac{73440}{24}=3060[/tex]2 males:
[tex]C2=\frac{10!}{2!\cdot(10-2)!}=\frac{10\cdot9\cdot8!}{2\cdot1\cdot8!}=\frac{90}{2}=45[/tex]4 females and 2 males: 3060* 45 = 137700
3rd option:
5 females:
[tex]C_{18,5}=\frac{18!}{5!\cdot(18-5)!}=\frac{18\cdot17\cdot16\cdot15\cdot14\cdot13!}{5\cdot4\cdot3\cdot2\cdot1\cdot13!}=\frac{1028160}{120}=8568[/tex]1 male:
[tex]C_{10,1}=\frac{10!}{1!\cdot(10-1)!}=\frac{10!}{1\cdot9!}=\frac{3628800}{362880}=10[/tex]5 females and 1 male = 8568 * 10 = 85680
4th option:
6 females and 0 male:
[tex]C_{18,6}=\frac{18!}{6!\cdot(18-6)!}=\frac{18\cdot17\cdot16\cdot15\cdot14\cdot13\cdot12!}{6\cdot5\cdot4\cdot3\cdot2\cdot1\cdot12!}=\frac{13366080}{720}=18564[/tex][tex]C_{10,0}=\frac{10!}{0!\cdot(10-0)!}=\frac{10!}{10!}=1[/tex]6 females and 0 male: 18564 * 1 = 18564
To finish the exercise, we have to sum the four options:
97920 + 137700 + 85680 + 18564 = 339864
So, right answer A: 339864.
