27
31
27
Mean: 24.43 Median: 24 Mode: 31, 18
26 / 31 x 100 = 74.193548 (or 74.2%)
23
2*100 + 31*10 + 27*1 = 200 + 310 + 27 = 537
23 25 27 29 31 33 35 37
24 occurs more than any other number, so it is the mode.
20
One possibility would be 27. I see here on the odd locations a growing series, adding 8 each time: 15 +8 = 23; 23 +8 = 31; 31 + 8 = 39 For the even locations, you could take a diminishing series, subtracting 4 each time: 35 - 4 = 31; 31 - 4 = 27.
17, 19, 23, 29 and 31 are prime. 15, 21, 25 and 27 are composite..