$2\mathrm{.}2$ Why is the analysis of algorithms often for the worst$-$case?

$2\mathrm{.}3$ Which method do you use to test if an element is in a set or list named x$?$

$2\mathrm{.}4$ Suppose list list$1$ is $1,2,5$ and list list$2$ is $2,3,6.$ After list$1.$addAll$($list$2)$; list$2$ is $$

$2\mathrm{.}5$ Suppose set $s1$ is $1,2,5$ and set $s2$ is $2,3,6.$ After $s1.$addAll$($s$2),$ s $1$ is $$