Today’s news reported that Sen. Kennedy’s surgery was successful. His surgeon told the press, “The surgery lasted roughly three and a half hours and is just the first step in Senator Kennedy’s treatment plan. One article reported that the surgery took about 31/2 hours. Notice there’s no space between whole number and fraction.
Another report said he was awake during the 3 1/2-hour procedure.
I suppose another report states the duration as 3.5 hours.
Whether using a fraction or decimal, each way shows how company style guides can and do differ. Clearly, the duration in the reports is the same; one style just writes it clearer.