Let the random variable X follow a normal distribution with \mu=80\

osi4a2nxk

osi4a2nxk

Answered question

2021-11-16

Let the random variable X follow a normal distribution with μ=80 and σ2=100.
a. Find the probability that X is greater than 60.
b. Find the probability that X is greater than 72 and less than 82.
c. Find the probability that X is less than 55.
d. The probability is 0.1 that X is greater than what number?
e. The probability is 0.6826 that X is in the symmetric interval about the mean between which two numbers?

Answer & Explanation

SaurbHurbkj

SaurbHurbkj

Beginner2021-11-17Added 16 answers

Step 1
Given:
XN(μ,σ)
μ=80
σ2=100
The standard deviation is calculated as
σ=σ2
=100
=10
Step 2
a. Probability that X is greater than 60
P(X>60)
=1P(X<60) (since the total probability is 1)
=1P(z<608010) (by standardizing)
=1P(x<2) (from the standard normal table P(x<2)=0.02275)
=10.02275
=0.97725
The probability that X is greater than 60 is 0.97725.
Step 3
b. Probability that X is greater than 72 and less than 82.
P(72<x<82)
=P(728010<z<828010) (by standardizing)
=P(0.8<z<0.2)
=P(x<0.2)P(x<0.8) (from the standard normal table P(x<0.2)=0.57926,P(x<0.8)=0.21186)
=0.579260.21186
=0.3674
Probability that X is greater than 72 and less than 82 is 0.3674.
Step 4
c.Probability that X is less than 55
P(x<55)
=P(z<558010) (by standardizing)
=P(z<2.5) (from the standard normal table P(x<2.5)=0.00621)
=0.00621
The probability that X is less than 55 is 0.00621.

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