Answer:
145.6 seconds
Step-by-step explanation:
Mean time (μ) = 120 seconds
Standard deviation (σ) = 20 seconds
In a normal distribution, the z-score for any time, X, is given by:
 [tex]z=\frac{X-\mu}{\sigma}[/tex]
The slowest 10% correspond to the 90th percentile of a normal distribution, which has a corresponding z-score of roughly 1.28. The lowest time that requires remedial training is:
[tex]1.28=\frac{X-120}{20}\\X=145.6\ seconds[/tex]
 Times of 145.6 seconds and over qualify for remedial training.
