Answer:
50%
Step-by-step explanation:
Recall : When given a normal or Symmetric distribution, the mean of the distribution is at the centre with 0.5 or 50% of the distribution to either side (right and left) of the distribution.
Hence, if the mean = 21 ; then the percentage of student body with atleast 21 years is the percentage to the left of the distribution, which is 50%.
Therefore, P(x ≤ 21) = 0.5 = 50%