In: Statistics and Probability
In a large introductory statistics lecture hall, the professor reports that 53% of the students enrolled have never taken a calculus course, 28% have taken only one semester of calculus, and the rest have taken two or more semesters of calculus. The professor randomly assigns students to groups of three to work on a project for the course. You are assigned to be part of a group. What is the probability that of your other two groupmates,
a) neither has studied calculus?
b) both have studied at least one semester of calculus?
c) at least one has had more than one semester of calculus?
As the students are randomly assigned to each group , thus event of of taking calculus course is independent of each other.
P( never taken Calculus) =0.53
P( one semester of Calculus) = 0.28
P( two or more semester of Calculus) = 0.19
a) P( neither has studied Calculus) = P( both never taken Calculus)
As events are independent
P( neither has studied Calculus) = 0.53 *0.53 = 0.2809
b) P( both have studied at least one semester of Calculus)
= P( both have studied one semester of Calculus) + P( both have studied two or more semester of Calculus)
+ P( either of them have studied one semester of Calculus and another two or more semester of Calculus)
= 0.28 *0.28 + 0.19*0.19 +2 *0.28*0.19
= 0.2209
c) P( atleast one have studied more than one semester of Calculus)
= P( either of them have studied two or more semester of Calculus and another one not )
+ P( both of them have studied two or more semester of Calculus )
= 2*0.19*(1-0.19 ) + 0.19*0.19
= 0.3439
Note : IF events A and B are independent
P( AB) =P( A ) *P( B)
Note : To find the following probabilities we multiplied by two , as the event can happen two ways
first person have studied one semester of Calculus and second two or more semester of Calculus
or
first person have studied wo or more semester of Calculus and second one semester of Calculus
P( either of them have studied one semester of Calculus and another two or more semester of Calculus)
= 0.19*0.28 +0.28 *0.19
Similarly
P( either of them have studied two or more semester of Calculus and another one not )