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No. Yes, you are missing something; see below.</p>
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The point is that 48 units at MIT is technically equivalent to 16 credits elsewhere; they both equate to taking four classes, so if you were to transfer out of MIT, you would receive only 16 credits at the new university for your 48-unit work at MIT. Therefore, a 12-unit class at MIT should have similar (predicted) time requirements and amount of work assigned as a 4-credit class at some other school. It’s the rigor of the course content that determines whether the 12-unit MIT course or the 4-credit other-school course is actually more difficult though.</p>