Example1.1
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Table1.2 shows data on sales compiled over several years by the accounting office for Eau Claire Auto Parts, a division of Major Motors. In this example, the year is the input variable, and total sales is the output. We say that total sales, \(S\text{,}\) is a function of \(t\text{.}\)
Year \((t)\) Total sales \((S)\) 2000 $612,000 2001 $663,000 2002 $692,000 2003 $749,000 2004 $904,000 Table1.2 -
Table1.3 gives the cost of sending printed material by first-class mail in 2016.
Weight in ounces \((w)\) Postage \((P)\) \(0 \lt w \le 1 \) $0.47 \(1 \lt w \le 2 \) $0.68 \(2 \lt w \le 3 \) $0.89 \(3 \lt w \le 4 \) $1.10 \(4 \lt w \le 5 \) $1.31 \(5 \lt w \le 6 \) $1.52 \(6 \lt w \le 7 \) $1.73 Table1.3 If we know the weight of the article being shipped, we can determine the required postage from Table1.3. For instance, a catalog weighing 4.5 ounces would require $1.31 in postage. In this example, \(w\) is the input variable and \(p\) is the output variable. We say that \(p\) is a function of \(w\text{.}\)
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Table1.4 records the age and cholesterol count for 20 patients tested in a hospital survey.
Age Cholesterol count Age Cholesterol count 53 217 \(51\) \(209\) 48 232 53 241 55 198 49 186 56 238 \(51\) \(216\) \(51\) \(227\) 57 208 52 264 52 248 53 195 50 214 47 203 56 271 48 212 53 193 50 234 48 172 Table1.4 According to these data, cholesterol count is not a function of age, because several patients who are the same age have different cholesterol levels. For example, three different patients are 51 years old but have cholesterol counts of 227, 209, and 216, respectively. Thus, we cannot determine a unique value of the output variable (cholesterol count) from the value of the input variable (age). Other factors besides age must influence a persons cholesterol count.