To solve this problem, we need to find the cumulative probability for $z = -0.91$ under the standard normal distribution curve. This is the area under the curve to the left of $z = -0.91$.

Steps:

1. Use the Standard Normal Table to look up the cumulative probability for $z = -0.91$.
2. Locate the row corresponding to $z = -0.9$ and the column for $0.01$. The intersection gives the cumulative probability.

From the standard normal table:

$P(Z \leq -0.91) = 0.1814$

Final Answer:

The probability is 0.1814.

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Would you like to see an explanation of how the standard normal table works, or any further calculations?

Here are 5 related questions for deeper understanding:

1. What is the probability of $z$ being greater than $-0.91$?
2. How do we find the probability for $z$ values greater than or equal to a given point?
3. What is the symmetry property of the standard normal distribution?
4. How is the z-score related to real-world applications like confidence intervals?
5. Can we calculate probabilities for non-standard normal distributions?

Tip: Always use the symmetry