Original practice · fully worked
Original variant: strongest calibration reading
Four independent calibration readings are uniformly distributed between 60 and 90. A technician records only the largest reading. Calculate its expected value.
- A
75.0 - B
80.0 - C
82.5 - D
84.0 - E
85.0
Answer and calculation
After scaling to Uniform(0,1), the maximum of four observations has mean 4/5. Mapping back to [60,90] gives 60 + 30(4/5) = 84, so choice D.
Setup
Setup
Standardize each reading to a unit-uniform variable.
Ui=30Xi−60∼Uniform(0,1) X(4)=60+30U(4) Model
Model
The maximum of four unit-uniform observations has density four times u cubed.
FU(4)(u)=u4,fU(4)(u)=4u3 Compute
Compute
Find the standardized expected maximum and transform it back to the original scale.
E[U(4)]=∫01u(4u3)du=54 E[X(4)]=60+30(54)=84 Answer
Answer
The expected strongest calibration reading is 84.
84.0(D)