Answer
Since the probability that a gestation period will last less than 224 days is less than 0.05, we can conclude that very preterm babies are unusual.
Work Step by Step
$\mu$ = 266, $\sigma$ = 16
Want to find $P( x < 224 )$
i) Convert 224 to a z-score:
z = $\frac{x - \mu}{\sigma}$
z = $\frac{224 - 266}{16}$
z= -2.63
ii) $P(x < 224) = P(z < -2.63) = 0.0043$
Since the probability that a gestation period will last less than 224 days is less than 0.05, we can conclude that very preterm babies are unusual.
