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According to the manual, a battery in a cellular phone loses 2% of its charge each day. Assume the battery is 100% charged.

a) Write an equation to represent the percent charge, P, as a function of the number of days, d, since the battery was charged.

b) Determine the number of days until the battery in only 50% charged.
 Mar 9, 2012

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rimmy:

a) Write an equation to represent the percent charge, P, as a function of the number of days, d, since the battery was charged.



P(d)=100-(1.02)^d
[input]plot( 100-(1.02)^d, d=0..200 )[/input]

rimmy:

Determine the number of days until the battery in only 50% charged.



100-(1.02)^d = 50
-(1.02)^d = 50-100
(1.02)^d = 50
log( 50, 1.02 )
[input]log( 50, 1.02 )[/input]
 Mar 9, 2012

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