We can see that Median/2 < Middle class income < 2*Median
     - In statement 2 we have minimum income given as  $18576.
     - This according to the question statement  should be half  the median(A middle class family is one           where the income is at least half the median family income).
     =>So, minimum income or Median/2 given in second statement, We can find the value of Median                and eventually 2*Median which is the maximum earning to be categorized into the Middle Class. 
          Hence from the income we can reach the Median and hence sufficient.
Statements 1 and 2 are telling us the same thing.
If the median income is $37,152, then the minimum income of a middle-class family 
HAS TO BE $18,576. And if the minimum income of a middle-class family is $18,576, then the median income HAS TO BE be $37,152