REVISION - The Format of a Formal Letter

[1] When an individual (SENDER) writes to an organisation such as a school or a company (RECIPIENT)  this is the way to set up the addresses for a FORMAL letter: 

Block 123 Bedok East Avenue 22 [When you write your address
#01-321                                            no need to mention your
Singapore 123456                           name at all]

9 July 2010

Mr. Ong Kim Soon        [Write the recipient's name]
The Principal                 [ Then write down his position]
St. Hilda's Secondary School
1 Tampines Road
Singapore 678910

[2]  When a school or a company (SENDER) writes to an individual (RECIPIENT),  this is the way to set up the addresses for a FORMAL letter:

Hwa Hin Electric Company
27 Raffles Drive 2
Singapore 678910

9 July 2010

Mr. Marvin Ng Chye Hin
Block 146  Bedok West Street 33
#09-123
Singapore 122345