Posted by Sam on .
Emily surmises that the probability that she will pass math or chemistry is .95, the probability of her passing math is .7, and the probability of passing both is .55. Find her estimate of the probability of passing chemistry?

math 
Reiny,
how about making a Venn diagram using 2 intersecting circles.
Place .55 in the intersection of the two.
Prob of passing math is .7 , but you already have put .55 in the math circle, that leaves .15 to go in the nonoverlapping part of math
label the nonoverlapping part of chemistry as x
then
x = .55 + .15 = .95
x = .25
so prob of passing chemistry is .55 + .25 = .8