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Reviewed CSCA Mathematics question · Hard

For a standard normal distribution, what is the approximate probability that a randomly selected value lies between -1.5 and 0.5?

  1. 0.6247
  2. 0.6915
  3. 0.7745
  4. 0.4332
Show the answer and explanation

Correct answer

A. 0.6247

Principle or equation

For a standard normal distribution, P(a < Z < b) = Φ(b) - Φ(a), where Φ is the cumulative distribution function.

Why this answer is correct

Using standard normal table: Φ(0.5) ≈ 0.6915, Φ(-1.5) ≈ 0.0668. Probability = 0.6915 - 0.0668 = 0.6247.

Example

P(-1 < Z < 1) ≈ 0.8413 - 0.1587 = 0.6826.

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