The average of 9 observations was 4, that of the 1st of 5 being 10 and that of the last 5 being 8. What was the 5th observation? Pick one:  A) 54  B) 12  C) 15  D) 17  E) 18
Explanation:   1 to 9 = 9 * 4= 
<gadget id="calculator">9 * 4</gadget>
<output>36</output>
36   1 to 5= 5 * 10= 
<gadget id="calculator">5 * 10</gadget>
<output>50</output>
50   5 to 9= 5 * 8= 
<gadget id="calculator">5 * 8</gadget>
<output>40</output>
40   5th= 50 + 40= 
<gadget id="calculator">50 + 40</gadget>
<output>90</output>
90 – 36= 54   Option 54
<result>A</result>
The average of 9 observations was 4, that of the 1st of 5 being 10 and that of the last 5 being 8. What was the 5th observation?