Question 316175
jim can do the job in 1/2 hour
so he does 2 job in 1 hour
..
sue does the same job in 3/4 hour
so she does 4/3 job in 1 hour
..
tony does the same job in 3/2 hours.
so he doe 2/3 job in 1 hour
..
together they can do 2 +4/3 + 2/3 job in 1 hour
LCM 3
6+4+2 /3 
=12/3 job in 1 hour
= 4 jobs in 1 hour.
so they do 1 job in 1/4 hour 
=15 minutes