If it takes two people 60 hours to build a fence how long will it take three people to do the same job

I believe that 40 hours could be correct using the above mentioned method however a percentage would tell you the answer is 30 hours, if you increase the personell on a job by 50% then the amount of time should also be reduced by 50 percent. 50%of 60 is 30. seems there are two ways to look at this.

It realistically could be any number based on the person but the most likely answer is 40 hours.