The average of 13 numbers is 15.8. If the average of the first seven numbers is 15.6 and that of the last seven numbers is 15.4,then the middle number is?	Choose one
A) 12.6
B) 11.6
C) 12.8
D) 12.9
E) 12.5
Middle number = 15.6*7 + 15.4*7- 15.8*13 = 109.2+107.8-205.4= 
<gadget id="calculator">109.2+107.8-205.4</gadget>
<output>11.6</output>
11.6   Answer is 11.6
<result>B</result>
The average of 13 numbers is 15.8. If the average of the first seven numbers is 15.6 and that of the last seven numbers is 15.4,then the middle number is?