It is 8/3.
5+7+9+12+12 = 45 and 45/5 = 9 which is the mean average
12+5+9+10=36/4=9 9 is the Mean of 12, 5, 9, and 10 To find the mean of something, add all the figures and then divide by the number of figures.
9
2 + 5 + 9 + 12 + 16 = 44/5 = 8.8
The mean of those data points is 9.
5
That is an infinite list. One such set is (5, 7, 9, 12, 12)
12/5 ÷ 12/9 = 12/5 x 9/12 = 9/5 = 14/5
If you mean: -3(n+5) = 12 then n works out as -9 because -3(-9+5) = 12
8+9+12+18+23/5=14
8.48528137424
They are 5, 7, 9 and 11.