1/2, 2/5, 3/5, 9/10 - please explain

If you look at the postings for other jobs you will notice that under "work status" some are per diem, some are full-time, while some are as you have quoted.
That means that :
1/2 =half time
2/5=.4 of full time
etc etc etc

As a new grad I was 4/5 that means 4 out of 5 days a week or 8 days in 2 weeks, after kids I worked 3/5( 3 out of 5 days or 6 days in two weeks) then I dropped to 1/2 time( 5 days in two weeks) then 2/5( two days a week or 4 days in 2 weeks) and now I am per diem.

It is so nice to have a flexible job!

http://www.elcaminohospital.org/body.cfm?id=83

Work Status:

At El Camino Hospital, pay periods are every two weeks. A full time position is 40 hours a week or 80 hours a pay period. Some positions are assigned less than 80 hours of work time in a pay period. Below is a guide to the work status designations at El Camino Hospital:

Full Time 80 hours per pay period
9/10 72 hours per pay period
4/5 64 hours per pay period
7/10 56 hours per pay period
3/5 48 hours per pay period
1/2 40 hours per pay period
2/5 32 hours per pay period
Per Diem Position is on-call with no set schedule. These positions are scheduled on an as-needed basis from 0 to 32 hours per week

Note: Most nurses at El Camino work 8 hour shifts although in a few depts there are 12 hour shifts. Hope that helps.