First, we are going to name each case:
S: a student taking a strength training gym class
C: a student taking a conditioning gym class
Then,
S AND C: the probability of taking a strength training gym class AND a conditioning gym class
(since "AND" is similar as an intersection, then this could be named S∩C)
S OR C: a student taking a strength training gym class OR a conditioning gym class
(since "OR" is similar as an union, then this could be named S∪C)
We want to find the probability of S OR C, this is
P(S∪C)
We have that the probability of each is given by:
P(S) = 0.90
P(C) = 0.20
P(S∩C) = 0.14
P(S∪C) = P(S) + P(C) − P(S∩C)
Since we want to find P(S∪C) using the information we have, then we replace:
P(S∪C) = P(S) + P(C) − P(S∩C)
↓
P(S∪C) = 0.90 + 0.20 − 0.14
P(S∪C) = 1.10 − 0.14
P(S∪C) = 0.96
Now, we have found the probability of a student taking a strength training gym class OR a conditioning gym class.