Consider the experiment of tossing 2 coins. Let A be the event of obtaining 2 heads and B, the event of obtaining 2 tails. Determine $A\cap B.$

Recall that the sample space S for tossing 2 coins is S = {HH, HT, TH, TT}. Hence, A = {HH} and B = {TT}. Note that there is no element common to both A and B. Thus, $A\cap B=\left\{\right\}.$