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Math·Advanced Math·Nonlinear functions

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490 points are awarded if the question is answered in fewer than 5 seconds. Each 5 seconds after that, the points decrease by 20% of the previous points.

Which function gives the number of points awarded for a correct answer $x$ seconds from the time the question is asked, where $x$ is a multiple of $5$?

A

$f(x)=490(0.80{)}^{x/5}$

B

$f(x)=490(0.80{)}^{5x}$

C

$f(x)=490(0.20{)}^{x/5}$

D

$f(x)=490(0.20{)}^{5x}$