The length $X$ of products manufactured at a certain factory follows a normal distribution with mean $m$ and standard deviation 4. When $\mathrm { P } ( m \leq X \leq a ) = 0.3413$, what is the probability that the sample mean of the lengths of 16 products randomly selected from this factory is at least $a - 2$, using the standard normal distribution table on the right? (where $a$ is a constant and the unit of length is cm) [4 points]
| $z$ | $\mathrm { P } ( 0 \leq Z \leq z )$ |
| 1.0 | 0.3413 |
| 1.5 | 0.4332 |
| 2.0 | 0.4772 |
(1) 0.0228
(2) 0.0668
(3) 0.0919
(4) 0.1359
(5) 0.1587