Allow me to correct you - they have NOT entered numeric data. They have input a string, the string might consist only of numbers - but they have entered a STRING, not a number. A string.

So, you want to count the number of rows whereby the string could safely be converted to a number vs the rows where that is not true.... (can you guess a pet peeve of mine? the storing of numbers or dates in strings and pretending they are numbers or dates.... they are not, they are just strings)

ops$tkyte%ORA10GR2> create or replace function is_number( p_string in varchar2 ) return varchar2
  2  is
  3          not_a_number exception;
  4          pragma exception_init( not_a_number, -6502 );
  5  begin
  6          if ( cast(p_string as number) is not null )
  7          then
  8                  return 'Y';
  9          end if;
 10  exception
 11          when not_a_number
 12          then
 13                  return 'N';
 14  end is_number;
 15  /

Function created.

ops$tkyte%ORA10GR2> column is_number format a10
ops$tkyte%ORA10GR2>
ops$tkyte%ORA10GR2> create table t as select decode( mod(rownum,2), 0, object_name, dbms_random.random ) string from all_objects;

Table created.

ops$tkyte%ORA10GR2> select is_number( string ) is_number, count(*) from t group by is_number( string );

IS_NUMBER    COUNT(*)
---------- ----------
Y               25129
N               25129