Jng-uistance telephone conversation. ASsume thal the density for X is given by f(x) = (1/10)e-x/10 x>0 (a) Verify that f is a density for a continuous random variable. (b) Assuming that f adequately describes the behavior of the random variable X, find the probability that a randomly selected call will last at most 7 minutes; at least 7 minutes; exactly 7 minutes. (c) Would it be unusual for a call to last between 1 and 2 minutes? Explain, based on the probability of this occurring. (d) Sketch the graph of f and indicate in the sketch the area corresponding to each of the probabilities found in part (b). 4. Some plastics in scrapped cars can be stripped out and broken down to recover the chemical components. The greatest success has been in processing the flex- ible polyurethane cushioning found in these cars. Let X denote the amount of this material, in pounds, found per car. Assume that the density for X is given by 1 1 f(x) = 25
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A percentage is a number indicated as a fraction of 100. It is a dimensionless number often expressed using the symbol %.
Algebraic Expressions
In mathematics, an algebraic expression consists of constant(s), variable(s), and mathematical operators. It is made up of terms.
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Numbers are some measures used for counting. They can be compared one with another to know its position in the number line and determine which one is greater or lesser than the other.
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Before we begin to understand the subtraction of algebraic expressions, we need to list out a few things that form the basis of algebra.
Addition
Before we begin to understand the addition of algebraic expressions, we need to list out a few things that form the basis of algebra.
#4 b
![Jng-uistance telephone conversation.
ASsume thal the
density for X is given by
f(x) = (1/10)e-x/10
x>0
(a) Verify that f is a density for a continuous random variable.
(b) Assuming that f adequately describes the behavior of the random variable
X, find the probability that a randomly selected call will last at most
7 minutes; at least 7 minutes; exactly 7 minutes.
(c) Would it be unusual for a call to last between 1 and 2 minutes? Explain,
based on the probability of this occurring.
(d) Sketch the graph of f and indicate in the sketch the area corresponding to
each of the probabilities found in part (b).
4. Some plastics in scrapped cars can be stripped out and broken down to recover
the chemical components. The greatest success has been in processing the flex-
ible polyurethane cushioning found in these cars. Let X denote the amount of
this material, in pounds, found per car. Assume that the density for X is given by
1 1
f(x) =
25 <x< 50
In 2 x
(a) Verify that f is a density for a continuous random variable.
(b) Usefto find the probability that a randomly selected auto will contain be-
tween 30 and 40 pounds of polyurethane cushioning.
(c) Sketch the graph of f, and indicate in the sketch the area corresponding to
the probability found in part (b).
5. (Continuous uniform distribution.) A random variable X is said to be uni-
formly distributed over an interval (a, b) if its density is given by
1
f(x) =
a<x<b
%3D
b- a
(a) Show that this is a density for a continuous random variable.
(b) Sketch the graph of the uniform density.
(c) Shade the area in the graph of part (b) that represents P[X< (a + b)/2].
(d) Find the probability pictured in part (c).
(e) Let (c, d) and (e, f) be subintervals of (a, b) of equal length. What is the re-
lationship between P[c <X sd] and P[e <X<f]? Generalize the idea
suggested by this example, thus justifying the name "uniform" distribution.
0. If a pair of coils were placed around a homing pigeon and a magnetic field
was applied that reverses the earth's field, it is thought that the bird would be-
come disoriented. Under these circumstances it is just as likely to fly in one
direction as any other, Let 0 denote the direction in radians of the bird's ini-
tial flight. See Fig. 4.18. 0 is uniformly distributed over the interval [0, 27].
(a) Find the density for 0.
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