The average of 11 numbers is 12.8. If the average of the first six numbers is 12.4 and that of the last six numbers is 12.2,then the middle number is?  Pick one.
A) 7.8  B) 7.9  C) 7.1  D) 7.2  E) 6.8
Middle number = 12.4*6 + 12.2*6 - 12.8*11 = 147.6-140.8= 
<gadget id="calculator">147.6-140.8</gadget>
<output>6.8</output>
6.8   Answer is 6.8
<result>E</result>
The average of 11 numbers is 12.8. If the average of the first six numbers is 12.4 and that of the last six numbers is 12.2,then the middle number is?