This Exam P sample reference tests Set Operations. Removing the triple region gives 82 in life-mutual only and 77 in annuity-mutual only, leaving 45 in mutual only. The exactly-one total then yields 100 in annuity only and 145 in life only; the remaining annuity-life region has 35. All seven regions total 500, choice D.
These notes identify the calculation error associated with each wrong letter when that error is reproducible.
AThe value 455 is the full total with the 45-client mutual-fund-only region omitted.
BThe value 495 falls five below the exact sum of the seven disjoint regions. It cannot reproduce the stated annuity, mutual-fund, and exactly-one totals.
CThe value 496 is an off-by-four region sum. The determined counts are integers 100, 45, 145, 77, 82, 35, and 16, whose sum is exactly 500.
EThe value 516 adds the 16-client triple intersection a second time after it has already been included in the disjoint partition.
Original practice · fully worked
Original variant: exactly one feature from conditional rates
A platform has 400 accounts. Fifty-five percent enable backups. Among backup-enabled accounts, 30% also enable encryption; among accounts without backups, 20% enable encryption. Calculate the number of accounts that enable exactly one of the two features.
A 66 accounts
B 102 accounts
C 154 accounts
D 190 accounts
E 256 accounts
Variant answer in brief
There are 220 backup-enabled accounts, of which 154 lack encryption. Of the 180 accounts without backups, 36 enable encryption. These two exactly-one regions total 190, choice D.
Setup
Setup
Split the account population by backup status.
n(B)=400(0.55)=220,n(Bc)=180
Model
Model
Calculate the two disjoint regions in which exactly one feature is enabled.
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