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Evaluate the following. In Exercises 17 and \(18,\) express the answer in terms of \(n .\) Do not use a calculator. $$\frac{8 !}{5 ! 3 !}$$

Short Answer

Expert verified
The value of \( \frac{8!}{5! \times 3!} \) is 56.

Step by step solution

01

Understand the Factorials

Factorials are products of an integer and all the integers below it down to 1. For example, \( n! = n \times (n-1) \times (n-2) \times \ldots \times 1 \). Here, \( 8! \) means multiplying 8 by all smaller integers down to 1, while \( 5! \) and \( 3! \) are similar for their respective numbers.
02

Write Factorials in Expanded Form

Expand the factorials. For \( 8! \), it is \( 8 \times 7 \times 6 \times 5 \times 4 \times 3 \times 2 \times 1 \). For \( 5! \), it is \( 5 \times 4 \times 3 \times 2 \times 1 \). For \( 3! \), it is \( 3 \times 2 \times 1 \).
03

Cancel Common Factors

Using the expanded form, divide and cancel the common factors from \( 5! \) and \( 3! \) in the numerator and denominator:\[\frac{8!}{5! \times 3!} = \frac{8 \times 7 \times 6 \times (5 \times 4 \times 3 \times 2 \times 1)}{(5 \times 4 \times 3 \times 2 \times 1) \times (3 \times 2 \times 1)}\]Cancel the \( 5 \times 4 \times 3 \times 2 \times 1 \) terms.
04

Simplify the Remaining Product

After cancellation, we are left with:\[\frac{8 \times 7 \times 6}{3 \times 2 \times 1}\]Simplify it step-by-step:1. \( 8 \div 2 = 4 \), so it becomes \( 4 \times 7 \times 6 \div 3 \).2. \( 6 \div 3 = 2 \), so it is \( 4 \times 7 \times 2 \).3. Calculate \( 4 \times 7 = 28 \), then \( 28 \times 2 = 56 \).
05

Final Result

Combine all the simplified parts to reach the final result. The expression \( \frac{8!}{5! \times 3!} \) simplifies to 56.

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Key Concepts

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

Combinatorics
Combinatorics is a fascinating branch of mathematics that deals with counting, arrangement, and combination of items. When you encounter expressions involving factorials, like \( \frac{8!}{5! \times 3!} \), you are diving into the world of permutations and combinations!

Factorials play an integral role in combinatorics. They help determine how many ways you can arrange or choose elements from a set. Here, the factorial notation "!" tells you the number of ways to arrange \( n \) distinct items.

For instance, \( n! \) (n factorial) is the number of ways to order \( n \) items. In combinatorial expressions like \( \frac{8!}{5! \times 3!} \), we are calculating combinations. This applies when choosing 3 items out of 8, without worrying about the order. What's amazing is how such a small formula elegantly balances complexity and simplicity, allowing you to solve large problems efficiently.
Integer Operations
Integer operations are fundamental in solving factorial problems efficiently. When working with factorials, you'll carry out operations like multiplication, division, and cancellation.

Understanding integer operations is crucial when calculating expressions such as \( \frac{8!}{5! \times 3!} \). Here, we multiply the integers from 1 up to 8, but only part of them actually needs multiplying.

By identifying common factors in the numerator and denominator (like \( 5! \)), we simplify computations considerably. Instead of multiplying all numbers and then dividing, integer operations help in breaking down the numbers and managing them smoothly. Integer operations, while basic, are indispensable for maintaining accuracy and ease when dealing with factorials.
Simplification
Simplification is a vital process in reducing expressions to their most manageable form. For example, the complex expression \( \frac{8!}{5! \times 3!} \) becomes more approachable when broken down.

Initially, \( 8! \) expands to \( 8 \times 7 \times 6 \times 5 \times 4 \times 3 \times 2 \times 1 \). But, you can simplify by canceling out \( 5 \times 4 \times 3 \times 2 \times 1 \) present in both the numerator and denominator.

This leaves you with \( 8 \times 7 \times 6 \div 3! \), which further reduces to a simpler product once you compute division and multiplication step-by-step. Simplification not only makes calculations less error-prone but also enhances understanding by focusing only on necessary numbers.
Algebraic Manipulation
Algebraic manipulation is akin to solving a puzzle. It involves rearranging, reducing, or rewriting expressions while preserving their value. In our case with factorials, we tweak the expression \( \frac{8!}{5! \times 3!} \) to make it less intimidating.

By expressing the factorials in expanded form, algebraic manipulation helps identify terms or factors that can cancel out. You can then re-arrange or simplify using basic arithmetic, leading to a clear solution. For instance, rewriting and cancelling terms allow us to streamline the method to find the expression's value effectively and accurately.

Algebraic manipulation blends abstract mathematics with concrete operations, providing insight and precision to solve and simplify problems like the one at hand.

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Most popular questions from this chapter

Find \(a_{1}\) for each arithmetic sequence. $$a_{6}=-8, a_{7}=-18$$

Find each sum that converges. $$\sum_{i=1}^{\infty}\left(-\frac{1}{3}\right)\left(\frac{3}{4}\right)^{i-1}$$

Use a formula to find the sum of each arithmetic series. $$1+2+3+4+\dots+50$$

Find the sum of the first 10 terms of each arithmetic sequence. $$8,6,4, \dots$$

What will happen when an infectious disease is introduced into a family? Suppose a family has \(I\) infected members and \(S\) members who are not infected, but are susceptible to contracting the disease. The probability \(P\) of \(k\) people not contracting the disease during a 1-week period can be calculated by the formula. $$P=\left(\begin{array}{l}S \\\k\end{array}\right) q^{k}(1-q)^{S-k}$$ where \(q=(1-p)^{l}\) and \(p\) is the probability that a susceptible person contracts the disease from an infectious person. For example, if \(p=0.5,\) then there is a \(50 \%\) chance that a susceptible person exposed to one infectious person for 1 week will contract the disease. (Source: Hoppensteadt, F. and C. Peskin, Mathematics in Medicine and the Life Sciences, Springer-Verlag.) (a) Approximate the probability \(P\) of 3 family members not becoming infected within 1 week if there are currently 2 infected and 4 susceptible members. Assume that \(p=0.1\) (b) A highly infectious disease can have \(p=0.5 .\) Repeat part (a) with this value of \(p\) (c) Approximate the probability that everyone would become sick in a large family if initially \(I=1, S=9\) and \(p=0.5\)

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