# Exp Function Word Problem

• May 19th 2009, 07:00 AM
skeske1234
Exp Function Word Problem
The probability, P, in percent, that a person will respond to a certain ad can be modelled by the equation P(n)=1-2^(-0.05n), where n is the number of days since the ad began on tv. After how many days is the probability greater than 20%?

my work:
0.20=1-2^(-0.05n)

then i solved for n, but i got a negative number.. what is wrong with my equation that i made and why
• May 19th 2009, 07:05 AM
mr fantastic
Quote:

Originally Posted by skeske1234
The probability, P, in percent, that a person will respond to a certain ad can be modelled by the equation P(n)=1-2^(-0.05n), where n is the number of days since the ad began on tv. After how many days is the probability greater than 20%?

my work:
0.20=1-2^(-0.05n)

then i solved for n, but i got a negative number.. what is wrong with my equation that i made and why

Start by solving $1-2^{-0.05 n} > 0.20 \Rightarrow -2^{-0.05 n} > -0.80 \Rightarrow 2^{-0.05 n} < 0.80$.

If you want more details it would be best to post the details of how you solved your inequation.