Mathematics High School

An article states that false-positives in polygraph tests (i.e., tests in which an individual fails even though he or she is telling the truth) are relatively common and occur about 15% of the time. Suppose that such a test is given to 10 trustworthy individuals. (Round all answers to four decimal places.)
(a) What is the probability that all 10 pass?
P(X = 10) =
(b) What is the probability that more than 2 fail, even though all are trustworthy?
P (more than 2 fail, even though all are trustworthy) =
(c) The article indicated that 400 FBI agents were required to take a polygraph test. Consider the random variable x = number of the 400 tested who fail. If all 400 agents tested are trustworthy, what are the mean and standard deviation of x?
Mean = 3
Standard deviation = 4

Answers

Answer 1

(a) To find the probability that all 10 trustworthy individuals pass the polygraph test,

we can use the binomial probability formula:

P(X = 10) = C(10, 10) * (0.15)^10 * (1 - 0.15)^(10 - 10)

Calculating the values:

C(10, 10) = 1 (since choosing all 10 out of 10 is only one possibility)

(0.15)^10 ≈ 0.0000000778

(1 - 0.15)^(10 - 10) = 1 (anything raised to the power of 0 is 1)

P(X = 10) ≈ 1 * 0.0000000778 * 1 ≈ 0.0000000778

The probability that all 10 trustworthy individuals pass the polygraph test is approximately 0.0000000778.

(b) To find the probability that more than 2 trustworthy individuals fail the test, we need to calculate the probability of exactly 0, 1, and 2 individuals failing and subtract it from 1 (to find the complementary probability).

P(more than 2 fail, even though all are trustworthy) = 1 - P(X = 0) - P(X = 1) - P(X = 2)

Using the binomial probability formula:

P(X = 0) = C(10, 0) * (0.15)^0 * (1 - 0.15)^(10 - 0)

P(X = 1) = C(10, 1) * (0.15)^1 * (1 - 0.15)^(10 - 1)

P(X = 2) = C(10, 2) * (0.15)^2 * (1 - 0.15)^(10 - 2)

Calculating the values:

C(10, 0) = 1

C(10, 1) = 10

C(10, 2) = 45

(0.15)^0 = 1

(0.15)^1 = 0.15

(0.15)^2 ≈ 0.0225

(1 - 0.15)^(10 - 0) = 0.85^10 ≈ 0.1967

(1 - 0.15)^(10 - 1) = 0.85^9 ≈ 0.2209

(1 - 0.15)^(10 - 2) = 0.85^8 ≈ 0.2476

P(more than 2 fail, even though all are trustworthy) = 1 - 1 * 0.1967 - 10 * 0.15 * 0.2209 - 45 * 0.0225 * 0.2476 ≈ 0.0004

The probability that more than 2 trustworthy individuals fail the polygraph test, even though all are trustworthy, is approximately 0.0004.

(c) The mean (expected value) of a binomial distribution is given by μ = np, where n is the number of trials (400 agents tested) and p is the probability of success (the probability of failing for a trustworthy agent, which is 0.15).

Mean = μ = np = 400 * 0.15 = 60

The standard deviation of a binomial distribution is given by σ = sqrt(np(1-p)).

Standard deviation = σ = sqrt(400 * 0.15 * (1 - 0.15)) ≈ 4

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Related Questions

Find the general solution to the following differential equations:
16y''-8y'+y=0
y"+y'-2y=0
y"+y'-2y = x^2

Answers

The general solution of the given differential equations are:

y = c₁e^(x/4) + c₂xe^(x/4) (for 16y''-8y'+y=0)

y = c₁e^x + c₂e^(-2x) (for y"+y'-2y=0)

y = c₁e^x + c₂e^(-2x) + (1/2)x

(for y"+y'-2y=x²)

Given differential equations are:

16y''-8y'+y=0

y"+y'-2y=0

y"+y'-2y = x²

To find the general solution to the given differential equations, we will solve these equations one by one.

(i) 16y'' - 8y' + y = 0

The characteristic equation is:

16m² - 8m + 1 = 0

Solving this quadratic equation, we get m = 1/4, 1/4

Hence, the general solution of the given differential equation is:

y = c₁e^(x/4) + c₂xe^(x/4)..................................................(1)

(ii) y" + y' - 2y = 0

The characteristic equation is:

m² + m - 2 = 0

Solving this quadratic equation, we get m = 1, -2

Hence, the general solution of the given differential equation is:

y = c₁e^x + c₂e^(-2x)..................................................(2)

(iii) y" + y' - 2y = x²

The characteristic equation is:

m² + m - 2 = 0

Solving this quadratic equation, we get m = 1, -2.

The complementary function (CF) of this differential equation is:

y = c₁e^x + c₂e^(-2x)..................................................(3)

Now, we will find the particular integral (PI). Let's assume that the PI of the differential equation is of the form:

y = Ax² + Bx + C

Substituting the value of y in the given differential equation, we get:

2A - 4A + 2Ax² + 4Ax - 2Ax² = x²

Equating the coefficients of x², x, and the constant terms on both sides, we get:

2A - 2A = 1,

4A - 4A = 0, and

2A = 0

Solving these equations, we get

A = 1/2,

B = 0, and

C = 0

Hence, the particular integral of the given differential equation is:

y = (1/2)x²..................................................(4)

The general solution of the given differential equation is the sum of CF and PI.

Hence, the general solution is:

y = c₁e^x + c₂e^(-2x) + (1/2)x²..................................................(5)

Conclusion: Therefore, the general solution of the given differential equations are:

y = c₁e^(x/4) + c₂xe^(x/4) (for 16y''-8y'+y=0)

y = c₁e^x + c₂e^(-2x) (for y"+y'-2y=0)

y = c₁e^x + c₂e^(-2x) + (1/2)x

(for y"+y'-2y=x²)

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The particular solution is: y = -1/2 x². The general solution is: y = c1 e^(-2x) + c2 e^(x) - 1/2 x²

The general solution of the given differential equations are:

Given differential equation: 16y'' - 8y' + y = 0

The auxiliary equation is: 16m² - 8m + 1 = 0

On solving the above quadratic equation, we get:

m = 1/4, 1/4

∴ General solution of the given differential equation is:

y = c1 e^(x/4) + c2 x e^(x/4)

Given differential equation: y" + y' - 2y = 0

The auxiliary equation is: m² + m - 2 = 0

On solving the above quadratic equation, we get:

m = -2, 1

∴ General solution of the given differential equation is:

y = c1 e^(-2x) + c2 e^(x)

Given differential equation: y" + y' - 2y = x²

The auxiliary equation is: m² + m - 2 = 0

On solving the above quadratic equation, we get:m = -2, 1

∴ The complementary solution is:y = c1 e^(-2x) + c2 e^(x)

Now we have to find the particular solution, let us assume the particular solution of the given differential equation:

y = ax² + bx + c

We will use the method of undetermined coefficients.

Substituting y in the differential equation:y" + y' - 2y = x²a(2) + 2a + b - 2ax² - 2bx - 2c = x²

Comparing the coefficients of x² on both sides, we get:-2a = 1

∴ a = -1/2

Comparing the coefficients of x on both sides, we get:-2b = 0 ∴ b = 0

Comparing the constant terms on both sides, we get:2c = 0 ∴ c = 0

Thus, the particular solution is: y = -1/2 x²

Now, the general solution is: y = c1 e^(-2x) + c2 e^(x) - 1/2 x²

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