can not convert to decimal(2,2)

Hi.  i have designed a form that user insert his educational information in it , so one of them is AverageMark. in my DB it's datatype is decimal(2,2). but when i want to insert it , Asp.net can not convert it to a valid decimal an will throw an exception , a part of my code is like this:   cmd.Parameters.Add("@Average", SqlDbType.Decimal).Value = Convert.ToDecimal(Average.Text.Trim()); i will be thank to solve the problem. ...