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A point is randomly selected on the surface of a lake that has a maximum depth of \(100 \mathrm{ft}\). Let \(y\) be the depth of the lake at the randomly chosen point. What are possible values of \(y\) ? Is \(y\) discrete or continuous?

Short Answer

Expert verified
The possible values of \(y\) (the depth of the lake at a randomly chosen point) range from 0 ft to 100 ft. And \(y\) is continuous, not discrete.

Step by step solution

01

Determining the range of the depth

As mentioned in the question, the lake has a maximum depth of 100 ft. It's also common knowledge that depth can't be a negative value. Therefore, the depth of the lake, \(y\), at any randomly chosen point can range anywhere from 0 ft (at the surface of the lake) to 100 ft (the maximum depth of the lake).
02

Determine the nature of the variable

The depth, \(y\), can take on any value within this range, not just distinct/separate values. For instance, it could be 17.5 ft, 43.2 ft, 60.9 ft etc. which are continuous fractions rather than discrete whole numbers. Therefore, \(y\) is a continuous variable, not discrete.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Probability Distribution
Probability distribution is a fundamental concept in statistics that describes how probabilities are assigned to different outcomes of a random variable. When dealing with continuous random variables, instead of individual probabilities (as seen with discrete variables), we talk about probability density functions (pdfs). This is because for continuous variables, each exact value has a probability of zero. Instead, we look at probabilities over intervals.

For example, in the context of the lake depth, the depth can take on any value between 0 and 100 feet, so it's a continuous variable. We would use a probability distribution to understand how likely it is to randomly select a point with certain depth values. While each exact depth (like exactly 20.5 feet) has a zero probability, intervals (like between 20 and 21 feet) have non-zero probabilities. This is captured by the area under the curve of the pdf over that interval.

Applying probability distributions helps in predicting and making informed decisions based on continuous data. Keep in mind that the shape and type of the probability distribution will fundamentally influence how we interpret the probabilities and data.
Continuous Data
Continuous data refers to variables that can take an infinite range of values within a given interval. Unlike discrete data, which consists of separate and distinct values, continuous data allow for fractional values. For example, when measuring the depth of a lake, you can have highly precise measurements like 45.67 ft or 33.89 ft.

Continuous data arises in situations where the measurement scale allows for infinite divisibility. In practical applications, this could mean any physical measurements like time, temperature, and, as in our exercise, depth. This data is real-valued and can be thought of as points on a continuum. Itemized observations are typically generated from measurements rather than counts.
  • This type of data supports more sophisticated statistical analyses.
  • It allows for the calculation of quantities such as mean, median, and mode with great precision.
  • Graphs like histograms and box plots can beautifully visualize continuous datasets.
Choosing how to handle continuous data is crucial because it impacts statistical modeling and the interpretation of variabilities within the data set.
Depth Measurement
Depth measurement is the process of determining the distance from the water surface to the bottom of the lake. In practical applications, this involves using tools like echo-sounders or measuring tapes, which provide precise depth readings.

In our exercise scenario, depth is measured as a continuous variable with any value between 0 ft (the surface) and 100 ft (the maximum depth of the lake). By demonstrating this range, we appreciate that depth measurement is not limited to whole numbers, offering fractions and decimals.

Key aspects of depth measurement in the context of continuous data include:
  • Understanding that precision is necessary in capturing accurate data.
  • Recognizing that depth is inherently non-negative.
  • Knowing that the measuring instrument's sensitivity will influence the smallest possible measurable difference, reflecting the tool's limit.
When interpreting depth data, continuous measurements allow a detailed view of the lake's underwater topography, crucial for various applications like environmental studies, navigation, and safety assessments.

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Most popular questions from this chapter

The time that it takes a randomly selected job applicant to perform a certain task has a distribution that can be approximated by a normal distribution with a mean value of \(120 \mathrm{sec}\) and a standard deviation of \(20 \mathrm{sec}\). The fastest \(10 \%\) are to be given advanced training. What task times qualify individuals for such training?

The lightbulbs used to provide exterior lighting for a large office building have an average lifetime of \(700 \mathrm{hr}\). If length of life is approximately normally distributed with a standard deviation of \(50 \mathrm{hr}\), how often should all the bulbs be replaced so that no more than \(20 \%\) of the bulbs will have already burned out?7.122 The lightbulbs used to provide exterior lighting for a large office building have an average lifetime of \(700 \mathrm{hr}\). If length of life is approximately normally distributed with a standard deviation of \(50 \mathrm{hr}\), how often should all the bulbs be replaced so that no more than \(20 \%\) of the bulbs will have already burned out?

The probability distribution of \(x\), the number of defective tires on a randomly selected automobile checked at a certain inspection station, is given in the following table: $$ \begin{array}{lrrrrr} x & 0 & 1 & 2 & 3 & 4 \\ p(x) & .54 & .16 & .06 & .04 & .20 \end{array} $$ a. Calculate the mean value of \(x\). b. What is the probability that \(x\) exceeds its mean value?

The following data are a sample of survival times (days from diagnosis) for patients suffering from chronic leukemia of a certain type (Statistical Methodology for Survival Time Studies [Bethesda, MD: National Cancer Institute, 1986\(]\) ): $$ \begin{array}{rrrrrrrr} 7 & 47 & 58 & 74 & 177 & 232 & 273 & 285 \\ 317 & 429 & 440 & 445 & 455 & 468 & 495 & 497 \\ 532 & 571 & 579 & 581 & 650 & 702 & 715 & 779 \\ 881 & 900 & 930 & 968 & 1077 & 1109 & 1314 & 1334 \\ 1367 & 1534 & 1712 & 1784 & 1877 & 1886 & 2045 & 2056 \\ 2260 & 2429 & 2509 & & & & & \end{array} $$ a. Construct a relative frequency distribution for this data set, and draw the corresponding histogram. b. Would you describe this histogram as having a positive or a negative skew? c. Would you recommend transforming the data? Explain.

A gasoline tank for a certain car is designed to hold 15 gal of gas. Suppose that the variable \(x=\) actual capacity of a randomly selected tank has a distribution that is well approximated by a normal curve with mean \(15.0 \mathrm{gal}\) and standard deviation \(0.1\) gal. a. What is the probability that a randomly selected tank will hold at most \(14.8\) gal? b. What is the probability that a randomly selected tank will hold between \(14.7\) and \(15.1\) gal? c. If two such tanks are independently selected, what is the probability that both hold at most 15 gal?

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