When considering the cost of roofing materials, many people take into account just the shingle prices. This is incorrect, as a roof made just of roofing shingles will not work. You also need to consider all the accessories that are included in a complete roof system.
Business letters tend to have both the sender and receiver's address and the date at the top of the page and they begin with a polite salutation, such as dear Mr. and Mrs, followed by a blank line before the body or the content of the letter.
Main Difference: The main difference between a formal letter and an informal letter is their purpose: a formal letter is written for professional (official and business) communication while the informal letter is used for personal communication. A letter is a written message from one party to another containing information.