farm out vs let out

farm out

verb
  • To subcontract (a task, responsibility, etc.) to another; to outsource. 

let out

verb
  • Of a school: to finish for the day or term, allowing the pupils to go home. 

  • To disclose. 

  • To rent out. 

  • Of sound, to emit. 

  • To allow to operate at higher speed by adjusting controls. 

  • To release. 

  • To enlarge by adjusting one or more seams. 

How often have the words farm out and let out occurred in a corpus of books? (source: Google Ngram Viewer )