12+9=21
21+15=36
36+13=49
49+6=55
If you have a list of numbers,5, 12, 15, 13, 3, 6,You add them all together,5+12+15+13+3+6 = 54And divide the sum by the amount of numbers (5, there are 5 numbers in the list)54 ÷ 5 = 10.810.8 is the mean number of 5, 12, 15, 13, 3, and 6
12-13-15 etc.... The sequence is add 1 then add 2
It is: 12+1 = 13
12 is a multiple of 6 and 1 is a factor of 12 and so 12+1 = 13
12+66=7878 divided by 6=13So the answer is 13
6
13 + 12 - 6 - 2 (16 plus 12 minus 6 minus 2) (13 + 12 = 25. 25 - 6 = 19. 19 - 2 = 17!
1 + 14 = 15 2 + 13 = 15 3 + 12 = 15 4 + 11 = 15 5 + 10 = 15 6 + 9 = 15 7 + 8 = 15 *There are more options with the use of negative integers
102.76
None of these will do the trick. 13+12-6-2 will however be 17.
54
13