Workout

Warm-up (1000)
4 x 250
...100 drill, 100 kick, 50 swim
...reverse IM order

Set (1000)
4 x 100 on 1:45 (build to steady pace) 
100 EZ 
4 x 100 on 1:45 (solid - controlled harder pace) 
100 EZ 

Set (400)
8 x 50’s choice on 1:30 
...odd (build to 90%)   
...even-moderate recovery 

Warm-down (200)
200 EZ