Answer
P(X > 0) = 0.7291. From this, we can conclude that if we take 100 samples, then 73 samples will have a positive monthly return rate.
Work Step by Step
Here we have n = 12
$σ_{x̅} = \frac{σ}{n} = \frac{0.04135 }{\sqrt 12} = 0.0012$
$z = \frac{x̅ - μ_{x̅}}{σ_{x̅}} = \frac{0 - 0.007233}{0.0012} = -0.61$
P(X > 0) = P(z > -0.61) = P(z < 0.61) = 0.7291
