John and Ling start their new jobs on the same day. John's schedule is six workdays followed by one day off. Ling's schedule is seven workdays followed by one day off. On how many days during their first year of work ($365$ days) do John and Ling have the same day off?
Every SEVENTH day is a day off for J ... L has every eigth day off... every 6x8 = 48 days they are both 'off'.
365/48 = ~7 times a year or possibly 8 times a year if they start off with the same day off at the early beginning of the year .