conditional probability of expected value for exponential distribution

Question

Let's assume that X is a random variable which follows exponential distribution. The expected value of this distribution is E . How can I compute the following probability:

$P(X\leq E)$

Thank you so much

Answer 1

The probability distribution function $P(X\le x)=1-e^{-kx}$. The density function $f(x)=ke^{-kx}$ The mean $E(X)=\int_0^{\infty}kxe^{-kx}dx=\frac{1}{k}$. You have $E=\frac{1}{k}$. Therefore $P(X\le E)=1-e^{-1}$.

The title mentions conditional probability. Where is it?