Original practice · fully worked
Original variant: conditional absolute sensor deviation
A robot arm's horizontal position X, in centimeters, has distribution function F(x)=(x/10)³ for 0<x<10. A monitor records the absolute deviation D=|X-4| from a target mark. Given that D is less than 3 centimeters, calculate the probability that D exceeds 1 centimeter.
- A
0.244 - B
0.287 - C
0.342 - D
0.667 - E
0.713
Answer and calculation
The condition D<3 restricts X to (1,7), while D>1 retains the two pieces (1,3) and (5,7). Their total probability is 0.244 within a conditioning probability of 0.342, giving 122/171=0.71345 and choice E.
Setup
Setup
Translate the observed absolute-deviation bound into an interval for the original position.
D<3⟺∣X−4∣<3 D<3⟺1<X<7 Model
Model
Within the conditioning interval, exceeding one centimeter of deviation produces two disjoint position ranges.
D>1⟺X<3 or X>5 {D>1}∩{D<3}={1<X<3}∪{5<X<7} Compute
Compute
Use CDF differences for the two favorable pieces and divide by the probability of the full conditioning interval.
Pr(D>1∣D<3)=F(7)−F(1)[F(3)−F(1)]+[F(7)−F(5)] Pr(D>1∣D<3)=0.343−0.001(0.027−0.001)+(0.343−0.125) Pr(D>1∣D<3)=0.3420.244=171122=0.7134502924… Answer
Answer
The conditional probability rounds to 0.713.
0.713(E)