Answer
See the explanation
Work Step by Step
a.
$1998 - 856$
$1999 - 1336$, from $1998$ to $1999$, $+480$
$2000 - 1578$, from $1999$ to $2000$, $+242$
$2001 - 1591$, from $2000$ to $2001$, $+13$,
Average = $\frac{480+242+13}{3}=245$,
b.
$2002-1483$,
$2003-994$, from $2002$ to $2003$, $-489$,
$2004-826$, from $2003$ to $2004$, $-168$,
Average = $\frac{-168-489}{2}=-328.5$
c.
The population was Increasing from $1997$ to $2001$
d.
The population was Decreasing from $2001$ to $2006$
