To complete a job a crew of 8 people needs 18 days. How long will the same job be finished if the crew will have 9 people?

First the you do 18/8 as it takes 8 people 18 days to finish the job. That gives you 2.25 days per person. Then subtract 2.25 from 18 since you have an extra person. 18-2.25=15 ...75 days is 18 hours. The answer is 15 days 18 hours.