Step-by-step explanation:
The probability that Aaron goes to the gym on exactly one of the two days= pro. that he goes on Saturday or pro. that he goes on Sunday
Prob. he goes on Saturday =0.8 while prob. that he goes on Sunday but not on Saturday = 0.9.
The prob. that Aaron goes to the gym either of the two days= 0.8 + 0.9 = 1.7
