Which sentence is more formal?
Merritt Electronics has a reputation for responding real quick to customer concerns and questions. Merritt Electronics has a reputation for responding quickly to all customer concerns and questions.
Formal writing is used for essays, business letters, and reports. The following types of informal language should be avoided in formal writing:
Type | Examples
slang | cool, awesome
idioms | knock your socks off
conversational language | gonna, kinda, yeah
abbreviated language | ASAP, FYI
overly simple or imprecise language | he got some stuff at the store
contractions | can't, won't
Contractions are not as informal as the other types, but they should be used sparingly in formal writing.
Compare the following sentences. The first is informal. The second is formal.
Informal: Yeah, ostriches can't fly, but they're awesome runners.
Formal: Though ostriches are flightless, they are remarkably adept runners.

The second sentence is less formal. You can tell because it uses conversational language (real quick).
The first sentence uses formal language in place of the conversational language, so it is more formal overall.