Question

The organizer of a conference is selecting workshops to include. She will select from 9 workshops about anthropology and 5 workshops about psychology. In
how many ways can she select 7 workshops if more than 4 must be about anthropology?​

Answer 1

Answer: She can select 7 workshops if more than 4 must be about anthropology in 1716 ways.

Step-by-step explanation:

Given, The organizer of a conference is selecting workshops to include. She will select from 9 workshops about anthropology and 5 workshops about psychology.

If he select 7 workshops if more than 4 must be about anthropology, the possible combinations = (5 anthropology, 2 psychology), (  6 anthropology, 1 psychology), (7 anthropology, 0 psychology)

Number of possible combinations = $^9C_5\times ^5C_2+^9C_6\times ^5C_1+^9C_7\times ^5C_0$

$=\dfrac{9!}{5!4!}\times\dfrac{5!}{2!3!}+\dfrac{9!}{6!3!}\times(5)+\dfrac{9!}{7!2!}\times (1)\\\\=\dfrac{9\times8\times7\times6}{4\times3\times2\times1}\times\dfrac{5\times4}{2}+\dfrac{9\times8\times7}{3\times2\times1}\times5+\dfrac{9\times8}{2}\\\\=1260+420+36\\\\=1716$  [using formula for combinations $^nC_r=\dfrac{n!}{r!(n-r)!}$]

Hence, she can select 7 workshops if more than 4 must be about anthropology in 1716 ways.