Question 349097
one worker 20 hours
1/20 of the job he will do in 1 hour
another worker 25 hours to do the job
1/25 of the job in 1 hour
...
Together they will do 1/20 + 1/25 of the job in 1 hour
LCD = 100
5+4 / 100 
9/100 of the job in 1 hour.
they will take 100 /9 hours to do the job.
=11.1 hours