All similar problems require the same basic logic, analytic solution, and units, but the computation will be different for each student. Thus students cannot simply copy the answer from each other. Multiple choice problems are randomly permuted to give different answers with multiple correct choices. The students receive immediate feedback. After submitting their answers the computer replies telling them whether their answer was correct or not.
Instructor usually permit the students to enter a solution multiple times.
Doing so allows for simple keyboarding errors and also encourages persistence as the student tries to find the errors and correct them. Normally each student is given a hard copy of the problem set or quiz that contains a numerical password. With the printed copy available, the students can solve the problems before going to the computer to submit their answers. In any event, they can read the problems with a computer connected to the internet. We use both methods of access at USC, but students seems to prefer the web-browser format.