This Exam P sample reference tests Independence. Exactly one event occurs in either the E-only or F-only region. Independence gives probabilities 0.294 and 0.104 for those disjoint regions, totaling 0.398, choice B.
These notes identify the calculation error associated with each wrong letter when that error is reproducible.
AThe value 0.056 is 0.16(0.35), the probability that neither event occurs.
CThe value 0.546 is 0.84(0.65), the probability that both events occur.
DThe value 0.650 is the marginal probability of F. It includes outcomes in which E also occurs.
EThe value 0.944 is the union probability 0.84+0.65-0.546. It includes the both-events region as well as exactly one.
Original practice · fully worked
Original variant: infer an independent detector rate from agreement
Two detectors operate independently. Detector A signals with probability 0.25, while detector B signals with unknown probability q. Their outputs agree, meaning both signal or neither signals, with probability 0.60. Calculate q.
A 0.15
B 0.25
C 0.30
D 0.40
E 0.60
Variant answer in brief
Agreement has probability 0.25q+0.75(1-q)=0.75-0.50q. Setting this equal to 0.60 gives q=0.30, choice C.
Setup
Setup
Represent agreement as the union of two disjoint matching-output cases.
The 3108-page Probability Proof Manual reorganizes 718 verified Exam P solutions by syllabus skill and adds formula proofs, error patterns, and original worked practice.