If it takes Daniel 9 hours to clean an office building and it takes Mark 6 hours, how long would it take the two of them, working together, to clean the building?

It would be 3 hours. This is 3 hours because the problem says that daniel takes 9 hours to clean and office building and mark takes 6 hours so if you subtract 9hours from 6 hours it would be 3 hours total. Now this can be 2 answers it can also be 15 hours if you were to add 9 hours to 6 hours.

Answer: it will take 3.6 hours

Step-by-step explanation:

If it takes Daniel 9 hours to clean an office building, it means that the rate at which he cleans the office building per hour is 1/9

If it takes Mark 6 hours to clean the office building, it means that the rate at which Mark cleans the office building per hour is 1/6

If they work together, they would work simultaneously and their individual rates are additive. This means that their combined working rate would be

1/9 + 1/6 = (6 + 9) / 54 = 15/54

Assuming it takes t hours for both of them to clean the office working together, the working rate per hour would be 1/t. Therefore,

15/54 = 1/t

t = 54/15 = 3.6 hours