Original practice · fully worked
Original variant: overlap of streaming memberships
Customers may subscribe to Music, News, or Sports, but News and Sports are mutually exclusive. Twenty percent have none, 60% have Music, 15% have News without Music, and 30% have exactly two services. Total News membership is twice total Sports membership. What percentage have both Music and Sports?
- A
5.00% - C
11.67% - B
15.00% - D
20.00% - E
30.00%
Answer and calculation
Let total Sports be s and total News 2s. The double-membership total is (2s-0.15)+(s-r_only); using the outside-Music partition identifies the requested overlap.
Setup
Setup
Partition customers outside Music into none, News-only, and Sports-only, using the mutual exclusion of News and Sports.
P(Mc)=0.40 P(none)=0.20 P(N∩Mc)=0.15 Model
Model
The outside-Music partition gives 5% Sports-only. Let total News membership be twice total Sports membership.
P(S∩Mc)=0.40−0.20−0.15=0.05 Compute
Compute
Express both two-service cells by subtracting the known single-service cells. The stated 30% total then gives Sports membership 1/6 and Music-plus-Sports membership 11.67%.
(2S−0.15)+(S−0.05)=0.30 P(M∩S)=61−0.05=0.116667 Answer
Answer
Therefore 11.67% have both Music and Sports, corresponding to choice C.
11.67%(C)