Complete answer:
Fulfill the requirements for a certain degree, a student can choose to take any 7 out of a list of 20 courses, with the constraint that at least 1 of the 7 courses must be a statistics course. Suppose that 5 of the 20 courses are statistics courses.
(a) How many choices are there for which 7 courses to take?
(b) Explain intuitively why the answer to (a) is not
Answer:
a) 71085 choices
b) See below
Step-by-step explanation:
a) First we're going to calculate in how many ways you can take 7 courses from a list of 20 without the constraint that at least 1 of the 7 courses must be a statistics course, that's simply a combination of elements without repetition so it's: , but now we should subtract from that all the possibilities when none of the courses chose are a statistic course, that's is
because 15 courses are not statistics and 7 are the ways to arrange them. So finally, the choices for which 7 courses to take with the constraint that at least 1 of the 7 courses must be a statistics course are:
b) It's important to note that the constraint at least 1 of the 7 courses must be a statistics course make the possible events dependent, we can not only fix an statistic course and choose the others willingly ( that is what means) because the selection of one course affect the other choices.