Aschool choir has 80 students; 36 of them are in seventh grade. also, 40 students in the choir are girls; 18 of them are in seventh grade. what is the probability that a student picked at random from the choir is either a girl or is in seventh grade? a. `27/40` b. `29/40` c. `13/40` d. `33/40`

B.  `29/40`

Step-by-step explanation:

These events are not mutually exclusive.  This means they can happen at the same time.

For two events A and B that are not mutually exclusive,

P(A or B) = P(A)+P(B) - P(A and B)

Our events are:

P(girl or 7th grade) = P(girl)+P(7th grade)-P(girl and 7th grade)

There are 40 girls out of 80 students:

P(girl or 7th grade) = 40/80+P(7th grade)-P(girl and 7th grade)

There are 36 7th graders in the choir out of 80 students:

P(girl or 7th grade) = 40/80+36/80-P(girl and 7th grade)

There are 18 7th grade girls in the choir:

P(girl or 7th grade) = 40/80+36/80-18/80 = 76/80-18/80 = 58/80

Both the numerator and denominator are divisible by 2:

(58÷2)/(80÷2) = 29/40