How many integers from 1 to 100 (both inclusive) have odd number of factors?
Pick one:  A) 7  B) 8  C) 9  D) 10  E) greater than 10

Rationale: all perfect squares have odd # of factors . squaring integers 1 - 10 produces 1 , 4 , 9 , 16 , . . . 100 which all have odd # of factors . answer is d
Answer: D