this will render staarting from frame 100 to 140 every 10 frames
You could also set the job as framelist : 1-1000x20, 1-1000x10, 1-1000x5, 1-1000
It will render first every 20 frame, then every 10 frame (skipping those already rendered), then every 5 frames (skipping those already rendered), then all other ones.
Frame per task will only work if frames are successive.