Answer :
Probability that a junior is in algbera or geometry = (Probability that a junior is in algbera + Probability that a junior is in geometry) - (Probability that the student is in both algbera and geometry)
Mathematically, we can rewrite the above statement as:
Pr(A or G) = Pr(A) + Pr(G) - P (A & G)
where A = Algbera
G = Geometry
Pr(A) Probability that a junior is in algbera = No of students in algebra class/ Total number of students
Pr(A) = 78/200 = 0.39
Pr(G) Probability that a junior is in geometry = No of students in geometry/ Total number of students
Pr (G) = 85/200 = 0.425
P ( A & G) Probability that the student is in both algebra and geometry = No of students in both algebra and geometry/ Total number of students
P(A & G) = 14/200 = 0.07
Pr(A or G) = (Pr(A) + Pr(G) ) - P (A & G)
Pr(A or G) = (0.39 + 0.425 ) - 0.07
Pr (A or G) = 0.815 - 0.07
= 0.745
Therefore the probability that a junior is in algbera or geometry is 0.745