How can I solve this problem?:

Question

Henry writes articles for 2 websites. He has a deadline every 9 days for one website, and a deadline every 12 days for the other one. On the last day of December he had a deadline for both websites. What is the next date on which he will have a deadline for both websites? (There are 31 days in January)

Answer 1

This seems to be more of a common multiple problem and the least common multiple for both 9 and 12 is 36.

36 days from December 31st would be February 5th.