typecasting numeric(18,4) to varchar/text

hi
how can i typecast a numeric(18,4) value (that i'm extracting from a table)
into a a varchar (which i'll be inserting into another table)
that is:

create table a (a numeric(18,4));
create table b (b varchar(25));
insert into a values(12000.43);
insert into b select (a.a)::varchar;


the above gives the followig error

ERROR:  Cannot cast type 'numeric' to 'character varying'

alternately try (this is my real requirement)

insert into b select 'ID'||((a.a)::varchar);

there has been no results on google

thanks in advance
ashok

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