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NHTSA crash tests. Refer to the NHTSA crash tests of new car models, Exercise 4.3 (p. 217). A summary of the driver-side star ratings for the 98 cars in the file is reproduced in the accompanying Minitab printout. Assume that one of the 98 cars is selected randomly and let x equal the number of stars in the car’s driver-side star rating.

  1. Use the information in the printout to find the probability distribution for x.
  2. FindP(x=5).
  3. FindP(x≤2).
  4. Find μ=E(x)and practically interpret the result.

Short Answer

Expert verified

a.

b. 0.1837

c.0.0408

d.3.9286

Step by step solution

01

(a) Formula for calculating P(x)

The formula for calculating the probability distribution isshown below:

P(x)=Probability100

Here role="math" localid="1653643443072" X,it represents the stars.

02

Computing the P(x)

The calculation P(x)is shown below:

Therefore, the probability distribution of the associated number of stars is 0.0408, 0.1735, 0.6020 and 0.1837.

03

(b) Formula for calculating P(x=5)

The formula for calculating the P(x=5)is shown below:

P(x=X)=Probability100

Here, asX it is equal to 5, the associated probability in percentage, 18.37, must be considered.

04

Computing the P(x=5)

The calculation P(x=5)is shown below:

P(x=5)=18.37100=0.1837

Therefore, the P(x=5) is 0.1837.

05

(c) Formula for calculating P(x≤2)

The formula for calculating the P(x≤2)is shown below:

P(x≤2)=P(x=0)+P(x=1)+P(x=2)

Here the summation of the probabilities fromX=0 toX=2 must be done.

06

Computing the P(x≤2)

The calculation P(x≤2)is shown below:

P(x≤2)=0100+0100+4.08100=4.08100=0.0408

Therefore, the P(x≤2) is 0.0408.

07

(d) Computing the μ=E(x)

μ=·¡(x)=E[xp(x)]=2×0.0408+3×0.1735+4×0.6020+5×0.1837=3.9286

Therefore, the μ=·¡(x) is 3.9286.

08

Interpretation of the value

The valueμ=·¡(x) is found to be 3.9286, which is the average. It indicates that whenever a car is selected at random, there will be a high probability for it to possess 3.9286 stars.

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