Answer:
12
Explanation:
mean = (sum of values)/(number of values)
Let x = missing value.
mean = (18 + 16 + x + 9 + 12 + 23)/6
(18 + 16 + x + 9 + 12 + 23)/6 = 15
78 + x = 90
x = 12
Answer: 12
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