Assume the random variable X is normally distributed with mean

Aryan Phillips

Aryan Phillips

Answered question

2022-02-12

Assume the random variable X is normally distributed with mean μ=50 and standard deviation σ=7. What is the probability P(X>42)?

Answer & Explanation

iloverayyeb

iloverayyeb

Beginner2022-02-13Added 14 answers

Step 1
We must standardise the Random Variable X with the Standardised Normal Distribution Z Variable using the relationship:
Z=Xμσ
And we will use Normal Distribution Tables of the function:
Φ(z)=P(Zz)
And so we get:
P(X>42)=P(Z>42507)
=P(Z87)
=P(Z1.1429)
If we look at this graphically it is the shaded part of this Standardised Normal Distribution:

By symmetry of the Standardised Normal Distribution it is the same as this shaded part

So:
P(Z>42)=P(Z1.1429)
=1P(Z<1.1429)
=1Φ(1.1429)
=10.8729 (from tables)
=0.1271

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