The speed limit is not a target. It is the maximum legal speed under ideal conditions, and almost every speed-limit question on the DMV permit test rewards the answer that respects the basic speed law over the answer that just matches the posted number.
Default speed limits
When no sign is posted, every state uses default "prima facie" limits: typically 25 mph in residential and business districts, 15-25 mph in school zones during school hours, and 55 mph on undivided rural highways. Interstates default to 65-70 mph in urban sections and 70-80 mph in rural sections, with Texas reaching 85 mph on a few corridors and Hawaii topping out at 60 mph.
The basic speed law
The basic speed law overrides every posted limit. It says no driver may operate a vehicle at a speed greater than is reasonable and prudent given current conditions — weather, visibility, traffic, road surface, and the presence of pedestrians or other hazards. [Recommended driving resource] An officer can cite you for going 55 in a 65 zone if rain or fog makes 55 unsafe, and the citation will hold up in court.
Why scenario questions matter
Most speed-limit questions on the permit test are scenario-based. "It is raining and traffic is slow on a 65 mph highway. The safest speed is..." — and the correct answer is always the slower one that respects the basic speed law. Memorize the defaults so you get the recall questions right; remember the basic speed law and you get the scenarios right too.
Minimum speeds
Most states also have minimum-speed rules. On Interstates and other limited-access highways, you may not drive so slowly that you block the normal and reasonable movement of traffic, except when reduced speed is necessary for safety. Drivers who insist on cruising in the left lane below the posted limit can be cited for impeding traffic.
School zones and work zones
School zones drop the limit to 15-25 mph when children are present or a beacon is flashing. Work zones often double the fine and apply whether or not workers are visible. Both are heavily enforced and both appear on every state's permit test.
How to study speed limits
Learn three numbers for your state: the residential default, the rural Interstate maximum, and the school-zone limit. Those three plus the basic speed law cover roughly 90% of the speed questions you'll see. The state-specific guides on PermitPrep list all four numbers for every state.