ANSWER: They are both the same.
DEC is short for DECIMAL (Base 10).
OCT is short for OCTAL (Base 8).
DEC 25 obviously is 25 in the decimal system.
OCT 31 is also 25 since 3 x 8 + 1 = 25.
For those who don't understand, here are the first 25 numbers in both bases (and you should know the first set):
DECIMAL: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25
OCTAL: 1, 2, 3, 4, 5, 6, 7, 10, 11, 12, 13, 14, 15, 16, 17, 20, 21, 22, 23, 24, 25, 26, 27, 30, 31