5lb book (3rd edition) Chapter 23, Question 44:
The probability of rain in Greg's town on Tuesday is 0.3. The probability that Greg's teacher will give him a pop quiz on Tuesday is 0.2. The events occur independently of each other.
Quantity A
The probability that either or both events occur
Quantity B
The probability that neither event occurs
I'm slightly confused with how Quantity A was calculated in the answer. Why was Quantity A calculated as 0.3+0.2 -(0.3)(0.2)=0.44? Isn't that how the prob of rain OR a quiz would be calculated? Why is the prob of "either or both" calculated the same way as just "either" would be calculated?