Exponential distribution $p\left ( x\right )=\lambda e^{-\lambda x}$ where mean and variance is $\frac{1}{\lambda },\frac{1}{\lambda }$
Now,
$84)$here mean=$2$
$p\left ( Y\geq t \right )=$$\frac{1}{2}.e^{-\frac{1}{2}.x}$
So, ans will be $(C)$
$85)$ In Exponential distribution $E\left ( x \right )=\mu$
Now, $E\left ( x_{1} \right )=\mu$
$E\left ( x_{2} \right )=\mu$
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then $E\left ( x_{n} \right )=E\left ( \frac{x_{1}+x_{2}+.....+x_{n}}{n} \right )$
Here
$E\left ( Y \right )=E\left ( \frac{\left ( X-2 \right )\cap \left ( X> 2 \right )}{X> 2} \right )$
Now putting $X=2$
$E\left ( 0 \right )=\mu =2$
Ans $D)$
