Agroup of students is donating blood during a blood drive. a student has 9/20 probability of having type 'o' blood and a 2/5 probability of having type 'a'.what is the probability that a student has type 'o' or type 'a' blood and why?

For the answer to the question above,
the answer is "The student can have only one blood type, so the actual events are mutually exclusive. "

The probabilities are not mutually exclusive. Based on the group 

P(Type O) = 9/20 = 45% or 0.45 
P(Type A) = 2/5 = 40% or 0.40 
P(Other) = 3/20 = 15% or 0.15
I hope my answer helped you. Feel free to ask more questions. Have a nice day!

Hello there.

A group of students is donating blood during a blood drive. a student has 9/20 probability of having type 'o' blood and a 2/5 probability of having type 'A'.what is the probability that a student has type 'o' or type 'a' blood and why?

The student can have only one blood type, so the actual events are mutually exclusive.