The probability of a woman exposed to German Measles will contract it is 0.2. If exposed to risk while pregnant the probability is 0.1 that the child will suffer a particular serious birth defect; otherwise the chances of this birth defect are 0.01. A child was born with this birth defect, what is the probability that the mother suffered from German Measles while pregnant?

I thought maybe it was p(german measles given that there was a birth defect) so [p(german measles + birth defect) divided by p(birth defect)] so [(.2+.11)/(.11)] but that gets me 2.8181 so that doesn't make sense.

Question

The probability of a woman exposed to German Measles will contract it is 0.2. If exposed to risk while pregnant the probability is 0.1 that the child will suffer a particular serious birth defect; otherwise the chances of this birth defect are 0.01. A child was born with this birth defect, what is the probability that the mother suffered from German Measles while pregnant?

I thought maybe it was p(german measles given that there was a birth defect) so [p(german measles + birth defect) divided by p(birth defect)] so [(.2+.11)/(.11)] but that gets me 2.8181 so that doesn't make sense.

anonymous · Answer

this is going to take a second, but it should definitely not be plus

dunnitagainn · Answer

you think multiplication? i wasn't sure which to use in this case.

dunnitagainn · Answer

@satellite73 you still there?

boldjon · Answer

Baby has it - > chance it got it without the mum having it is 0.01
Chance the mum had it has to be 1 - 0.01 = 0.99

boldjon · Answer

The key point is that the probability of a defect is 0.1 if the mother is exposed, but not infected. If the mother is exposed her chance of getting infected is 0.2.

dunnitagainn · Answer

@boldjon i don't follow, are you saying that the answer is just 1-p(mom didn't have it while pregnant) because that is waaaaaay easier than i was making it out to be lol