(Modeling) Distance from the Origin of the Nile River The Nile River in Africa is about 4000 mi long. The Nile begins as an outlet of Lake Victoria at an altitude of 7000 ft above sea level and empties into the Mediterranean Sea at sea level (0 ft). The distance from its origin in thousands of miles is related to its height above sea level in thousands of feet (x) by the following formula. Distance = (7 − x) / (0.639x + 1.75) For example, when the river is at an altitude of 600 ft, x = 0.6 (thousand), and the distance from the origin is Distance ≈ (7 − 0.6) / (0.639 × 0.6 + 1.75) ≈ 3, which represents 3000 mi. (Data from The World Almanac and Book of Facts.) What is the distance from the origin of the Nile when the river has an altitude of 7000 ft?
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1
Identify the given altitude of the Nile River, which is 7000 ft. Since the formula uses altitude in thousands of feet, convert this value to thousands by dividing by 1000: \(x = \frac{7000}{1000} = 7\).
Write down the formula for the distance from the origin in terms of \(x\):
\(\text{Distance} = \frac{7 - x}{0.639x + 1.75}\).
Substitute the value \(x = 7\) into the formula:
\(\text{Distance} = \frac{7 - 7}{0.639 \times 7 + 1.75}\).
Simplify the numerator and denominator separately:
- Numerator: \$7 - 7$
- Denominator: \(0.639 \times 7 + 1.75\).
Calculate the fraction by dividing the simplified numerator by the simplified denominator to find the distance in thousands of miles from the origin of the Nile River.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Understanding the Given Formula
The formula relates the altitude of the Nile River (in thousands of feet) to its distance from the origin (in thousands of miles). It is a rational function where the numerator and denominator both depend on the altitude variable x. Interpreting and correctly substituting values into this formula is essential to find the distance for a given altitude.
The problem uses scaled units: altitude is given in thousands of feet and distance in thousands of miles. Recognizing this scaling is crucial to correctly interpret the values and results. For example, an altitude of 7000 ft corresponds to x = 7, and a distance result of 3 means 3000 miles.
The formula is a ratio of two expressions involving x. To solve the problem, one must substitute the given x value into both numerator and denominator, then perform division carefully. Understanding how to evaluate such rational expressions accurately is key to obtaining the correct distance.