SQL & PL/SQL :: Conversion Varchar2 To Number

I have 2 tables.The column in table A is number and Column in table B is a varchar2 datatype.I have to use the Column of table B as a filter to column of Table A.Below is the example.

create table A(Col1 number);
Inert into A values(1);
Inert into A values(2);
Inert into A values(3);
Inert into A values(4);

Create table B(Col1 Varchar2(100));
Insert into b value ('1,2,3');

Select * from A where col1 in (select col1 from b)
Error: Invalid Number

Is there a way to convert the varchar to number.The varchar field have multiple characters (numbers) seperated by commas.