Answer
There is a 10% chance of the mean time being 10.8 minutes or less.
Work Step by Step
Here n = 40, p = 0.10. Using Table V of the book, we have:
z = -1.28
$σ_{x̅} = \frac{σ}{\sqrt n} = \frac{3.2}{40} = 0.51$
$z = \frac{x̅ - μ_{x̅}}{σ_{x̅}}$
$x = zσ_{x̅} + μ_{x̅} = -1.28 \times 3.2 + 11.4 = 10.8$
