Step-by-step explanation:
God said "let there be light" The people who made the calendar said "Let there be Friday 13th.
Answer:
-1/12
Multiples of 4 are: 4, 8, 12, 16, 20, 24, 28, 32, 36, ...
Multiples of 6 are: 6, 12, 18, 24, 30, 36, ...