The average of 9 observations was 6, that of the 1st of 5 being 10 and that of the last 5 being 8. What was the 5th observation?  Options:
A) 36  B) 12  C) 15  D) 17  E) 18
Explanation:   1 to 9 = 9 * 6= 
<gadget id="calculator">9 * 6</gadget>
<output>54</output>
54   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 – 54= 36   Option 36
<result>A</result>
The average of 9 observations was 6, that of the 1st of 5 being 10 and that of the last 5 being 8. What was the 5th observation?