Answer
(a.) Total U.S. population $ =2.9x+236 $.
(b.) $308.5$ million.
(c.) Underestimates by 0.5 million.
Work Step by Step
The given two functions are
For male U.S. population $ M(x)=1.5x+115 $.
where, $ M(x) $ is in millions and $ x $ is number of years after $ 1985 $.
For female U.S. population $ F(x)=1.4x+121 $.
Where, $ F(x) $ is in millions and $ x $ is number of years after $ 1985 $.
(a.) Total U.S. population $ T(x)=M(x)+F(x) $.
$ T(x)=1.5x+115+1.4x+121 $.
Add like terms.
$T(x)= 2.9x+236 $.
(b.) The value of $ x $ for U.S. population in $ 2010 $.
$ x=2010-1985 =25 $
Substitute into the function of total U.S. population.
$ T(25)=2.9(25)+236 $.
$ T(25)=308.5 $.
(c.) Actual total U.S. population in $ 2010 $ is
$ = 152+157 $
$ =309 $
The result in part (b) underestimate the actual value by.
$ =309-308.5 $
$ =0.5 $.
