# Math Help - Logarithms word problem

1. ## Logarithms word problem

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

2. Originally Posted by casey_k
The probability, P, in percent, that a person will respond to a certain advertisement can be modeled by the equation P(n) = 1 - 2^ -0.05n, where n is the number of days since the advertisement began on television. After how many days is the probability greater than 20%?
Put P(n) = 0.2 and solve.

$n = -\frac{20log(1-P(n))}{log(2)}$