Well the task is as follows.
About two events A and B, we know that $P(A)=\frac{1}{6}$ and $P(B)=\frac{2}{7}$. Find $P(A \cup B)$
a) If A and B is disjunktive
b) If A and B is independent
My solutions
a) $\frac{1}{6}+\frac{2}{7}$
b) $\frac{1}{6}+\frac{2}{7} - (\frac{1}{6} \times \frac{2}{7})$
This gives the correct answer but I'm not 110% sure why.
And, the same problem with another task.
For a girl to be colorblind both her parents needs to carry the gene for it. She inherits the gene from both parents independently. The probability is 8% that the girl gets that gene from the mother and 8% for she to get it from the father.
What is the probability that one girl is colorblind?
What is the probability that one girl is not colorblind?
The first one is just: $0.08^2$. That's fine.
The second one is $0.92+0.92 - 0.92^2$
I don't understand why the second isn't just $0.92^2$ like the first one.