Final answer:
For the standard normal probability distribution, 50% of the curve lies to the left of the mean.
Step-by-step explanation:
In a standard normal probability distribution, also known as the Z-distribution, the mean is 0 and the standard deviation is 1. The area to the left of the mean represents the values that are less than the mean. Since the mean is in the center of the distribution, 50% of the curve lies to the left of the mean.