Answer
$\mathrm{a}$.
Independent variable: $a$, dependent variable: $P$
$\mathrm{b}$.
$P(20)=231.427$
In 2012 there are 231.427 million Americans who are 20 years of age or older.
$\mathrm{c}$.
$P(0)=327.287$
In 2012 there are 327.237 million Americans
Work Step by Step
$\mathrm{a}$.
$P$ changes when a changes, a is arbitrary.
Independent variable: $a$,
dependent variable: $P$
$\mathrm{b}$.
a=20 means the people observed are 20 years of age or older.
Substitute a=20 into the expression:
$P(20)=0.014(20)^{2}-5.073(20)+327.287$
$=5.6-101.46+327.287$
$=231.427$ (million)
In 2012 there are 231.427 million Americans who are 20 years of age or older.
$\mathrm{c}$.
a=0 means the people observed are 0 years of age or older,
meaning that all people are observed.
Substitute a=0 into the expression:
$P(0)=0.014(0)^{2}-5.073(0)+327.287$
$=327.287$ (million)
In 2012 there are 327.237 million Americans.
