Question 329023
Fred & jill together can do a job in 4 hours
so tthwy do 1/4 of the job in 1 hour
..
jill can do the job in 10 hours
she does 1/10 of the job in 1 hour
..
Fred will do 1/4 -1/10 of the job in 1 hour
LCD = 20
5-2 / 20 = 3/20
so fred can do the job alone  in 20/3 hours 
=6.66 hours