Answer
P(X < 10) = 0.0028. This implies that if we take 1000 samples of size 40, 3 samples will have a mean time of 10 minutes or less.
Work Step by Step
Here we have n = 40
$σ_{x̅} = \frac{σ}{n} = \frac{3.2 }{\sqrt 40} = 0.51$
$z = \frac{x̅ - μ_{x̅}}{σ_{x̅}} = \frac{10-11.4}{0.51} = -2.75$
P(X < 10) = P(z < -2.75) = P(z > 2.75) = 0.0028
