math
posted by Sha .
Thomas in 4 hours. Julia can do the same job in 6 hours. How many hours will it take the two of them to do the job if they work together?

Assuming there is no change in productivity..
In one hour, Thomas does 1/4=25% of the job, while Julia does 1/6=16.66%. Combined they would do 25%+16.66% = 41.66% of the job in 1 hour. So, 1/.4166= 2.4 hours