Suppose the chances of picking up a cold from someone by shaking hands with them is .01 (assuming you don’t know whether they have a cold or not), and that each encounter you have is independent of any others. You go to a party and shake the hands of 20 people. What is the probability that you'll catch a cold?

Question

anonymous · Answer

100%
       82%
       50%
       18%
       2%
       0%

anonymous · Answer

i guess we have to interpret the problem to say 
what is the probability that at least one of the people you shake hands will give you a cold

anonymous · Answer

the probability that you get it from any given person is $.01$ so the probability you do not is $.99$
if you do it twenty times, the probability you do not get the cold is $.99^{20}$

anonymous · Answer

So its 0%

anonymous · Answer

i doubt it

anonymous · Answer

did you compute $.99^{20}$?

anonymous · Answer

Its 82% thanks!

anonymous · Answer

hold on that is not the answer!

anonymous · Answer

that is the probability that you do NOT get a cold
if the probability you do not get a cold is $.82$ then the probability that you DO get a cold (which is what is asked) is $1-.82=.18$

anonymous · Answer

Oh I was trying to solve for the wrong thing. Thanks for catching that :)

anonymous · Answer

yw