The number 8 is repeated at least once; the numbers add up to 5*12=60 because there are 5 numbers and the mean is 12; the median is the middle number. If we subtract 10 from the sum of 60, we have 50. At least two 8's are in the dataset, and we can see that because the median is 10 there can only be two 8's. So subtract 16 from 50 and we have 34. The two numbers left add up to 34, and they must be different from one another, so we have 0 and 34; 1 and 33; 2 and 32, and so on. If we pick 16 and 18 the dataset will be 8 8 10 16 18. The mean is 12; mode is 8; median is 10. But we could also have picked {8 8 10 15 19}, {8 8 10 14 20},...{8 8 10 11 23}.