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Answer:
x must be 13
Step-by-step explanation:
Represent the nine scores by a, b, c, d, e, f, g, h, i.
Write the following equation to indicate that the average of these nine scores is 8:
a+b+c+d+e+f+g+h+i
----------------------------- = 8, or a+b+c+d+e+f+g+h+i = 72 if we multiply both
9 sides of this equation by 9.
Next, we add scores x and x+ 1 to
a+b+c+d+e+f+g+h+i + x + x + 1
and divide the result by 11, as there are now 11 scores instead of just 9:
a+b+c+d+e+f+g+h+i + x + x + 1
----------------------------------------------
11
Earlier, we saw that a+b+c+d+e+f+g+h+i = 72. We can now replace
a+b+c+d+e+f+g+h+i in the above fraction by 72:
72 + 2x + 1
------------------- = 9 (as the new average is 9)
11
Multiplying both sides of this equation by 11 results in:
73 + 2x = 99, or 2x = 26.
Then x must be 13, and x + 1 must be 14.