Event Certainty

[shangwuvn]

Please help.
Can it be concluded that if there is a 50% chance of contracting a communicable disease through contact with an infected person, there would be a 100% chance of contracting the disease if two contacts were made with the infected person?
Thanks for your help.

[JohnM]

No, there would be a 50% chance on each contact. If you had two contacts, then the possible outcomes are:

1 = contracting the disease
0 = not contracting the disease

Possible Outcomes for 2 contacts:

0, 0 --> P(0,0) = 0.25
0, 1 --> P(0,1) = 0.25
1 --> P(1,na) = 0.50

So, the chances of getting the disease after 2 contacts is:
P(0,1) or P(1,na) = P(0,1) + P(1,na) = 0.75