Started a db backup at 10.10 AM & required 20 min for completion. @10.25 AM we inserted few rows in a table. Will new data be there in backup db?

After Backup You wont have these records which newly inserted.

You won't find newly inserted row in backup copy, but the newly inserted will be in primary db

It's impossible because when you start Backing up the database it will take the last one before the backup process began

It should be possible in the Case of RDBMS like Oracle.

DB in Two Layers i.e. Logical and Physical would help serve the purpose.

Thanks

once you issue the backup command it will backup the data at the time of command given, so the new data won't be in the backup but it will be inserted in the table.

No, the records inserted 10.25 will be in the database log and the database as well if it is committed, but it will not be in the database backup. 

The newly inserted data will not be available because when backup is started, all tables are locked. hence new record will not be available in the backup.