4 . A population of eagles P t can be modelled by the equation Pt � P0 e kt
, where
P
0 is the initial population , and t is measured in decades . After one decade , it is estimated that 20P1�17 P0
� 0. It is given that one decade is equivalent to ten years .
( a ) Show that k � ln 0.85 .
( b ) Find the least number of whole years for which
[ 2 ]
P t
0.5 P � . 0
[ 5 ]
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