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Adult male height and weight: Here is a rule of thumb relating weight to height among adult males: If a man is 1 inch taller than another, then we expect him to be heavier by 5 pounds. a. Explain why, according to this rule of thumb, among typical adult males the weight is a linear function of the height. Identify the slope of this function. b. A related rule of thumb is that a typical man who is 70 inches tall weighs 170 pounds. On the basis of these two rules of thumb, use a formula to express the trend giving weight as a linear function of height. (Be sure to identify the meaning of the letters that you use.) c. If a man weighs 152 pounds, how tall would you expect him to be? d. An atypical man is 75 inches tall and weighs 190 pounds. In terms of the trend formula you found in part b, is he heavy or light for his height?

Short Answer

Expert verified
The weight is a linear function of height with a slope of 5. The formula is \( W = 5H - 180 \). A 152-pound man is about 66.4 inches tall. The 75-inch man is light for his height.

Step by step solution

01

Identifying the Relationship

The rule states that if a man is 1 inch taller, he is expected to be 5 pounds heavier. This suggests a consistent increase in weight with an increase in height, demonstrating a linear relationship. The slope of this linear function is the change in weight per unit change in height, which is 5 pounds per inch.
02

Defining the Formula

Using the second rule of thumb, a man who is 70 inches tall weighs 170 pounds. Denoting weight by \( W \) and height by \( H \), the linear function can be expressed as \( W = mH + b \). From above, the slope \( m \) is 5, and using the point \((70, 170)\), we substitute to find \( b \). Thus, \( 170 = 5(70) + b \). Solving gives \( b = -180 \). The formula is \( W = 5H - 180 \).
03

Calculating Height from Weight

Given \( W = 152 \) pounds, substitute in the formula: \( 152 = 5H - 180 \). Solving for \( H \), we get \( 5H = 332 \) which gives \( H = 66.4 \) inches.
04

Evaluating the Atypical Man

For a man who is 75 inches tall, we calculate the expected weight using the formula. \( W = 5(75) - 180 = 195 \) pounds. Comparing to his actual weight, 190 pounds, this man is 5 pounds lighter than expected according to the trend.

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Key Concepts

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

Slope
The concept of slope is foundational in understanding linear functions. Slope is essentially a measure of how steep a line is. It represents how much the dependent variable (in this case, weight) changes for a unit increase in the independent variable (height). In mathematical terms, it is often expressed as "rise over run," indicating how much the value on the vertical axis (rise) changes relative to a change on the horizontal axis (run).

In the exercise's context, the rule of thumb states that if a man is 1 inch taller, he is expected to be 5 pounds heavier. This implies a direct, linear relationship between height and weight. Therefore, the slope of the function is 5. It shows that for every inch increase in height, there is an expected increase of 5 pounds in weight. This slope of 5 confirms a consistent pattern: one-inch change in height results in five additional pounds.

Slope is a crucial element because it allows us to make predictions about one variable based on changes in another. Whether you're addressing height and weight or any other linear relationship, slope gives you the power to model and predict based on consistent changes.
Weight and Height Relationship
Weight and height have a well-known correlation, especially among adults. The exercise discusses a specific pattern established through a rule of thumb: a linear relationship indicating that weight increases with height at a consistent rate. It helps in understanding and forecasting weight based on height. This correlation is depicted through a linear model, which simplifies predicting unknown data. In this case, predicting the weight of a person given their height.

Consider these points:
  • The 5-pound increase per additional inch signifies that taller adult males generally have higher weights.
  • This relationship assumes a consistent linear increase throughout different height ranges. Hence, as you know one male's height, you can reasonably guess his weight!
  • Using the rule that a 70-inch male typically weighs 170 pounds, you can set a reference point to build and verify a comprehensive model.
By applying such rules, you get a clear picture of statistical trends which emerge due to natural body characteristics. It emphasizes that even biological patterns can be approached with mathematical precision, leading to insightful conclusions.
Modeling with Linear Equations
Linear equations are powerful tools for modeling real-world phenomena, like the weight-height relationship in adult males discussed in the exercise. Through linear equations, you can create predictive models that simplify and clarify how variables relate to one another.

In this exercise, a linear equation is derived from the general form \[W = mH + b\]where:
  • \(W\) is the weight.
  • \(H\) is the height.
  • \(m\) is the slope (5 in our scenario).
  • \(b\) is the y-intercept, which was calculated to be -180.
This equation \(W = 5H - 180\)acts as a practical model. It allows calculating the weight from knowing the height, supporting scenarios like estimating a height based on a known weight or assessing whether a person weighs more or less than this model predicts.

Modeling with equations like these makes complex data intuitive. They provide a broad understanding that serves decision-making, such as evaluating deviations in weight and height norms for health assessments or fitness planning.

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Most popular questions from this chapter

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