Chapter 16: Problem 23
A machine purchased for \(\$ 75,000\) is expected to decrease in value by 20\(\%\) each year. The value of the machine after \(n\) years is \(75,000(1-0.20)^{n} .\) Use the binomial theorem to express the value of the machine after 5 years in sigma notation.
Short Answer
Expert verified
The value of the machine after 5 years is $24,576.
Step by step solution
01
Expression Analysis
The problem gives us the formula for the value of the machine after \(n\) years: \(75,000(1-0.20)^{n}\). It wants us to use the binomial theorem to express this for \(n = 5\), which means we need to expand \((1-0.20)^5\) using binomial expansion.
02
Binomial Theorem Formula
Recall the binomial theorem which states that \((a+b)^n = \sum_{k=0}^{n} \binom{n}{k} a^{n-k} b^k\). Here, \(a = 1\), \(b = -0.20\), and \(n = 5\). We will express \((1-0.20)^5\) in this manner.
03
Expand the Expression
Applying the binomial theorem, we have:\[(1 - 0.20)^5 = \sum_{k=0}^{5} \binom{5}{k} (1)^{5-k}(-0.20)^k.\] Calculate the binomial coefficients, which are values of \(\binom{5}{k}\).
04
Calculate Binomial Coefficients
Calculate each coefficient:- \(\binom{5}{0} = 1\)- \(\binom{5}{1} = 5\)- \(\binom{5}{2} = 10\)- \(\binom{5}{3} = 10\)- \(\binom{5}{4} = 5\)- \(\binom{5}{5} = 1\).
05
Substitute Coefficients and Simplify
Substitute values into the expanded expression:\[(1 - 0.20)^5 = 1 - 5(0.20) + 10(0.20)^2 - 10(0.20)^3 + 5(0.20)^4 - (0.20)^5.\]Simplify each term to express as a series in sigma notation.
06
Simplify Each Term
Calculate each term:- \((0.20)^0 = 1\) results in \(1\)- \(-5(0.20)^1 = -1\)- \(10(0.20)^2 = 0.40\)- \(-10(0.20)^3 = -0.08\)- \(5(0.20)^4 = 0.0064\)- \(-(0.20)^5 = -0.00032\).
07
Express in Sigma Notation
Express the series in sigma notation:\[(1 - 0.20)^5 = \sum_{k=0}^{5} \binom{5}{k} (1)^{5-k}(-0.20)^k = 0.32768.\]
08
Calculate Value After 5 Years
The problem statement asks for the initial machine value times the binomial expansion result:\[ \text{Value after 5 years} = 75,000 \times (1-0.20)^5 = 75,000 \times 0.32768 = 24,576. \]
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Exponential Decay
Exponential decay describes a process where the value decreases by a consistent percentage over equal time intervals. A common real-world example is the decreasing value of a machine, like the one initially valued at $75,000. Each year, the machine loses 20% of its current value. This is represented by the formula: \[75,000(1-0.20)^n\] where \(n\) is the number of years.
- "Exponentially" indicates that the change is multiplicative, not linear.
- The decay factor is \(1-0.20 = 0.80\). Each year, the value is 80% of the previous year's value.
Sigma Notation
Sigma notation provides a concise way to write long sums. It's a great tool in mathematics for representing series. The expression \(\sum_{k=0}^{5} \binom{5}{k} (1)^{5-k}(-0.20)^k\) is a sigma notation. Each term in the series is summed for \(k\) from 0 to 5.
- \(\Sigma\) stands for "sum up" and is the capital Greek letter Sigma.
- The numbers below and above \(\Sigma\) represent starting and ending values, respectively.
- The expression to the right of \(\Sigma\) is the general term for each step (here, based on binomial theorem).
Binomial Coefficients
Binomial coefficients \(\binom{n}{k}\) are the heart of the binomial theorem. These coefficients determine the weights of each term in the expansion of a binomial expression. For example, in the expression \((1 - 0.20)^5\):
- \(n=5\) is the total number of terms minus one.
- The coefficients are calculated using the formula \(\frac{n!}{k!(n-k)!}\).