In a competitive examination, top 4 amongst 100 contestants are to be selected. A highly valid and reliable test is available, but it can give results in terms of ranks, not quantitative scores. Also, only 10 contestants can be included at a time in a test. Limited number of test sets are available, and any of the test sets cannot be reused. Device a strategy to identify top 4 contestants, using minimum number of different test sets, each using exactly once for only 10 contestants. How many minimum number of sets will be required?