Exponential distribution function. I am having trouble with this question as well. Any help or hints will be really appreciated.
On a TV game show contestants have to complete a particular task. Suppose that the time take for a typical contestant to complete the task is a random variable with an exponential distribution sigma=2, measured in minutes. This means that the probability density is given by.
$$f(x)=\left\{
\begin{array}{lr}
\frac{1}{2}e^{-\frac{x}{2}} & x ≥0\\
0 & \text{otherwise}
\end{array}
\right.
$$
a) Calculate the probability that a typical contestant fails to complete the task in 3 minutes.
b) Calculate the probability that a contestant takes over 2 minutes to complete the task given that they do not fail
I keep getting the wrong answers for both of a and b .Any sort of hint for me to understand this better would be really appreciated . 
thanks

For the first question, try integrating that distribution from 3 to $\infty$. This is the probability that the contestant takes 3 minutes or more to complete the task.
For the second question, I'm going to assume that it is considered a failure if the contestant takes more than 3 minutes to complete a task. In this case, integrate the same distribution from 2 to 3 this time.
Does this make sense?
