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Consider the discrete probability distribution shown here.

x

10

12

18

20

p

.2

.3

.1

.4

a. Calculate,2 and .

b. What isP(x<15) ?

c. Calculate 2 .

d. What is the probability that xis in the interval 2 ?

Short Answer

Expert verified

(a) =15.4,2=18.44and=4.294.

(b) Px<15=0.5

(c) 2=(6.812,23.988)

(d) The required probability is 0.5.

Step by step solution

01

Given information

X is a random variable.

02

Identifying the type of random variable

a.

Mean=

=i=14xjPxi=100.2+120.3+180.1+200.4=2+3.6+1.8+8=15.4

Variance=2

2=i=14x-2Px=1015.420.2+12-15.420.3+18-15.420.1+20-15.420.4=29.160.2+11.560.3+6.760.1+21.160.4=5.832+3.468+0.676+8.464=18.44

Standard Deviation=

=18.44=4.294

Hence, =15.4,2=18.44 and =4.294 .

03

When  p(x<15)

b.

px<15=px=10+px=12=0.2+0.3=0.5

Hence, Px<15=0.5

04

Calculating the value when  μ±2σ

c.

The interval is

2=15.424.294=15.48.588=6.812,23.988

05

Calculating P (x) when μ±2σ

d.

P6.812x23.988=P0x17.176=1-Px17.176=1-Px=18+Px=20=1-0.1+0.4=1-0.5=0.5

Hence, the required probability is 0.5.

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