I was trying to complete this question, but I'm confused about where either but not both comes in:

"certain chickens on a large farm have developed diseases, 2% have fatty liver syndrome, 3% have cage layer fatigue. 4% of the chickens have either one of these conditions, but not both"

a) Find the percentage of poultry with both conditions

b) a chicken is selected at random from this farm, what is the probability it has neither condition?

Calling 'fatty liver syndrome' event A, and 'cage layer fatigue' event B

What I have understood so far is that:

P(A)=0.02

P(B)=0.03

P(A) + P(B) = 0.04

Where this fits in a Venn diagram, I'm not too sure- since they are not mutually exclusive, there is P(AnB), but using the addition rule requires P(AuB), the conditions of which mean that A and B occur together, which is not equal to 0.04?

thanks!