pay dirt vs problem

pay dirt

noun
  • A profitable area or period; success. 

  • Earth which contains profitable quantities of ore. 

problem

noun
  • A difficulty that has to be resolved or dealt with. 

  • A puzzling circumstance. 

  • A set of moves required to complete a climb. 

  • A question to be answered, schoolwork exercise. 

  • Objection. 

  • Difficulty in accepting or understanding or refusal to accept or understand. 

adj
  • Causing a problem; problematic; troublesome. 

  • Difficult to train or guide; unruly. 

How often have the words pay dirt and problem occurred in a corpus of books? (source: Google Ngram Viewer )