<h2>mean = 13.67</h2>
<u>Step-by-step explanation:</u>
<h3><u>o</u><u>b</u><u>s</u><u>e</u><u>r</u><u>v</u><u>a</u><u>t</u><u>i</u><u>o</u><u>n</u><u>s</u><u> </u>= 4, 21, 13, 17, 5, 9, 10, 20, 19, 12, 20, 14</h3>
<h2>
mean = sum of observations ÷ numbers of observations</h2><h2>...........................................</h2><h3>sum of observation = 4+21+13+17+5+9+10+20+19+12+20+14</h3><h3>= <u>164</u></h3>
<h3><u>n</u><u>u</u><u>m</u><u>b</u><u>e</u><u>r</u><u>s</u> of observation = 12</h3>
<h2>mean = 164 ÷ 12</h2><h2> = 13.67</h2>