Final answer:
Fire extinguishers are not rated using numbers and letters. The labeling system used is the National Fire Protection Agency (NFPA) 704 Hazard Identification System.
Step-by-step explanation:
The statement 'An extinguisher is rated using numbers and letters' is False. Fire extinguishers are actually rated using a color-coded labeling system known as the National Fire Protection Agency (NFPA) 704 Hazard Identification System. This system uses a diamond-shaped label to provide information about the fire, health, and reactivity hazards of the extinguishing agent. The numbers and letters you may be referring to are typically found on the label of the extinguisher indicating the type and class of fire it is suitable for.