You have two numbers at the ends, 12 and -16. When you insert 3 arithmetic means between them, you will have 4 intervals/segments between -16 and 12. The full length of the segment [-16,12] is 12 - (-16) = 12 + 16 = 28. Hence, the length of each smallest interval/segment between the neighbor values will be= 7. So, your sequense is -16, -16+7 = -9, -9+7 = -2, -2+7 = 5 and 5 +7 = 12. Answer. The three arithmetic means to insert are -9, -2, and 5.