So here is the summary for the question: 100 women use a new pregnancy test, 44 of the women are actually pregnant. Of the women who are pregnant, 35 test positive. Of the women who are not pregnant, 8 of them test positive. Calculate the probability for each event.
Did I get this question right? Here is the question: A randomly selected test is negative, given the woman is not pregnant.
I got: $P(\text{Negative|Not Pregnant})
= \frac{56}{66} = 0.85$
Is this correct?
Best Answer
You have enough data to make a complete cross-tabulation:
$$\begin{array}{r|c|c|c} &\text{pos.}&\text{neg.}&\text{total}\\ \hline \text{pregnant}&35&9&44\\ \hline \text{not pregnant}&8&48&56\\ \hline \text{total}&43&57&100 \end{array}$$
There are $56$ women who are not pregnant, and $48$ of them test negative, so the probability that a randomly chosen non-pregnant woman tests negative is
$$\frac{48}{56}=\frac67=0.\overline{857142}\;.$$
This is slightly larger than your $\frac{56}{66}=\frac{28}{33}=0.\overline{84}$.