Answer: The value to add to the set is 52
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For a moment, ignore the extra value we'll add in later.
The given set of values add to -34.
Let x be the extra value we add in. It adds to the -34 to get -34+x, then we divide by 6 because the set {-4,-10,-16,8,-12,x} has 6 items.
So we get the mean (-34+x)/6
Set this equal to the mean we want (3) and solve for x
(-34+x)/6 = 3
-34+x = 6*3
-34+x = 18
x = 18+34
x = 52
The set {-4,-10,-16,8,-12,x} updates to {-4,-10,-16,8,-12,52} and this set has a mean of 3.
