# Math Help - Exponential Distribution

1. ## Exponential Distribution

Hi

The following question i don't understand why my answer is incorrect.
X is an exponential rc, with mean 2. What is the Pr(X < 2.5)?
$F(x) = 1$ - e^( $\lambda x$)

$\lambda = 2$ and x = 2.5

so $1$ - e^(-2*2.5)

P.S

2. ## Re: Exponential Distribution

Originally Posted by Paymemoney
Hi

The following question i don't understand why my answer is incorrect.
X is an exponential rc, with mean 2. What is the Pr(X < 2.5)?
$F(x) = 1$ - e^( $\lambda x$) That should be minus lambda
$\lambda = 2$ and x = 2.5
so $1$ - e^(-2*2.5)
The mean is $1 / \lambda$, so if the mean is 2, then lambda is...