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Complete Question
At one point the average price of regular unleaded gasoline was ​$3.39 per gallon. Assume that the standard deviation price per gallon is ​$0.07 per gallon and use​ Chebyshev's inequality to answer the following.
​(a) What percentage of gasoline stations had prices within 3 standard deviations of the​ mean?
​(b) What percentage of gasoline stations had prices within 2.5 standard deviations of the​ mean? What are the gasoline prices that are within 2.5 standard deviations of the​ mean?
​(c) What is the minimum percentage of gasoline stations that had prices between ​$3.11 and ​$3.67​?
Answer:
a) 88.89% lies with 3 standard deviations of the mean
b) i) 84% lies within 2.5 standard deviations of the mean
ii) the gasoline prices that are within 2.5 standard deviations of the​ mean is $3.215 and $3.565
c) 93.75%
Step-by-step explanation:
Chebyshev's theorem is shown below.
1) Chebyshev's theorem states for any k > 1, at least 1-1/k² of the data lies within k standard deviations of the mean.
As stated, the value of k must be greater than 1.
2) At least 75% or 3/4 of the data for a set of numbers lies within 2 standard deviations of the mean. The number could be greater.μ - 2σ and μ + 2σ.
3) At least 88.89% or 8/9 of a data set lies within 3 standard deviations of the mean.μ - 3σ and μ + 3σ.
4) At least 93.75% of a data set lies within 4 standard deviations of the mean.μ - 4σ and μ + 4σ.
​
(a) What percentage of gasoline stations had prices within 3 standard deviations of the​ mean?
We solve using the first rule of the theorem
1) Chebyshev's theorem states for any k > 1, at least 1-1/k² of the data lies within k standard deviations of the mean.
As stated, the value of k must be greater than 1.
Hence, k = 3
1 - 1/k²
= 1 - 1/3²
= 1 - 1/9
= 9 - 1/ 9
= 8/9
Therefore, the percentage of gasoline stations had prices within 3 standard deviations of the​ mean is 88.89%
​(b) What percentage of gasoline stations had prices within 2.5 standard deviations of the​ mean?
We solve using the first rule of the theorem
1) Chebyshev's theorem states for any k > 1, at least 1-1/k² of the data lies within k standard deviations of the mean.
As stated, the value of k must be greater than 1.
Hence, k = 3
1 - 1/k²
= 1 - 1/2.5²
= 1 - 1/6.25
= 6.25 - 1/ 6.25
= 5.25/6.25
We convert to percentage
= 5.25/6.25 × 100%
= 0.84 × 100%
= 84 %
Therefore, the percentage of gasoline stations had prices within 2.5 standard deviations of the​ mean is 84%
What are the gasoline prices that are within 2.5 standard deviations of the​ mean?
We have from the question, the mean =$3.39
Standard deviation = 0.07
μ - 2.5σ
$3.39 - 2.5 × 0.07
= $3.215
μ + 2.5σ
$3.39 + 2.5 × 0.07
= $3.565
Therefore, the gasoline prices that are within 2.5 standard deviations of the​ mean is $3.215 and $3.565
​(c) What is the minimum percentage of gasoline stations that had prices between ​$3.11 and ​$3.67​?
the mean =$3.39
Standard deviation = 0.07
Applying the 2nd rule
2) At least 75% or 3/4 of the data for a set of numbers lies within 2 standard deviations of the mean. The number could be greater.μ - 2σ and μ + 2σ.
the mean =$3.39
Standard deviation = 0.07
μ - 2σ and μ + 2σ.
$3.39 - 2 × 0.07 = $3.25
$3.39 + 2× 0.07 = $3.53
Applying the third rule
3) At least 88.89% or 8/9 of a data set lies within 3 standard deviations of the mean.μ - 3σ and μ + 3σ.
$3.39 - 3 × 0.07 = $3.18
$3.39 + 3 × 0.07 = $3.6
Applying the 4th rule
4) At least 93.75% of a data set lies within 4 standard deviations of the mean.μ - 4σ and μ + 4σ.
$3.39 - 4 × 0.07 = $3.11
$3.39 + 4 × 0.07 = $3.67
Therefore, from the above calculation we can see that the minimum percentage of gasoline stations that had prices between ​$3.11 and ​$3.67​ corresponds to at least 93.75% of a data set because it lies within 4 standard deviations of the mean.
