The average of 9 observations was 8, that of the 1st of 5 being 10 and that of the last 5 being 8. What was the 5th observation?	Choose one.
A) 18 B) 12 C) 15 D) 17 E) 19
Explanation:   1 to 9 = 8 * 9= 
<gadget id="calculator">8 * 9</gadget>
<output>72</output>
72   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 – 72= 18   Option 18
<result>A</result>
The average of 9 observations was 8, that of the 1st of 5 being 10 and that of the last 5 being 8. What was the 5th observation?