Inserting four arithmetic means to these numbers will form an arithmetic sequence with first term equal to 40 and sixth term equal to 10. The common difference (d) is calculated by,
d = (a6 - a1) / (6 - 1)
d = (10 - 40) / (6 - 1) = -6
Thus, the difference between two successive terms in the sequence should be -6. The four arithmetic means are therefore: 34, 28, 22, and 16.
