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You want to calculate the probability that a normally distributed variable with mean 0 and variance 1 lies between -1 and 1 using erf. Which formula correctly computes this probability?

hard📝 Application Q15 of 15
SciPy - Constants and Special Functions
You want to calculate the probability that a normally distributed variable with mean 0 and variance 1 lies between -1 and 1 using erf. Which formula correctly computes this probability?
A0.5 * (erf(1) + erf(-1))
Berf(1) - erf(-1)
C0.5 * (erf(1 / sqrt(2)) - erf(-1 / sqrt(2)))
Derf(1 / 2) - erf(-1 / 2)
Step-by-Step Solution
Solution:
  1. Step 1: Recall normal distribution probability formula using erf

    Probability between a and b for standard normal is 0.5*(erf(b/sqrt(2)) - erf(a/sqrt(2))).
  2. Step 2: Apply formula for a=-1, b=1

    Plugging in gives 0.5*(erf(1/sqrt(2)) - erf(-1/sqrt(2))).
  3. Final Answer:

    0.5 * (erf(1 / sqrt(2)) - erf(-1 / sqrt(2))) -> Option C
  4. Quick Check:

    Use erf(x/sqrt(2)) formula = A [OK]
Quick Trick: Divide limits by sqrt(2) before erf, multiply difference by 0.5 [OK]
Common Mistakes:
MISTAKES
  • Using erf directly without dividing by sqrt(2)
  • Adding erf values instead of subtracting
  • Ignoring the 0.5 multiplier

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