• If the variable X follows a normal distribution with mean μ and standard deviation σ, we write X ~ N(μ, σ²).
• We convert it to a standard variable using the formula:

Z = (X − μ) ÷ σ

1. Then P(X ≥ c) = P(Z ≥ (c − μ) ÷ σ), and we complete the solution from the table.
2. The value of Z is called the standard score (z-score).
3. It tells us how many standard deviations the value lies above or below the mean.