The Reaction Time Game
JavaScript, ES6 352 340 335 bytes, Potential score : 2 + 8 + 12 + 4 + 4 + 8 = 38
&lt;script&gt;r=Math.random,s=setTimeout;T=N=0;a=_=&gt;(S=s(_=&gt;(C=eval(G.innerHTML=((k=~~(r()*5))+~~(r()*5))+'-'+k),t=new Date,R=s(_=&gt;C=G.innerHTML=a(clearTimeout(S)),r()*1e3)),r()*2e3+1e3),'');document.onkeyup=E=&gt;{clearTimeout(R);E.key==C&amp;&amp;++N&amp;&amp;(T+=(X=new Date-t))&amp;&amp;alert([X,N%10?'':T/10]);C=G.innerHTML=a(N%10||(T=0))};a()&lt;/script&gt;&lt;a id='G'/&gt;

or try this JSFiddle on latest Firefox.
Working:

Shows a random question in form of X-Y after a random interval of [2,4] seconds.
Waits for a keypress till a random time in an interval of [1,2] seconds, after which, clears the input and moves to step 1.
If correct number is pressed, alerts the time in milliseconds.
If this is the tenth (or rather every tenth) correct answer, show the average time in milliseconds for the last 10 correct answers after a comma.
Empties the input area, goes to Step 1 again.

Please comment if something is incorrect or if you have any doubts.