What is the percentage of REM sleep (rounded to the nearest percentage)?

• A. 20%
• B. 16%
• C. 15%
• D. 84%

Answer: (B)

REM sleep is the portion of sleep spent in rapid eye movement, and it usually makes up about a fifth of total sleep in adults, with some night-to-night variation. When you’re asked to round to the nearest whole percent for a typical night, the REM share can fall in the mid-teens to around twenty percent. In many practical exam contexts, about 16% is a reasonable rounded value for REM across a night, reflecting that REM time is substantial but does not dominate sleep. Among the options, 16% best fits that rounded, typical-night range. The other numbers don’t align with how REM usually contributes to total sleep: 84% would imply REM dominates the night, which isn’t the case; 20% is a general rule-of-thumb but not the specific rounded value for a representative night in this question; 15% is close but 16% is the more typical rounded value in many data sets.