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CBSE Questions for Class 12 Commerce Applied Mathematics Probability Distribution And Its Mean And Variance Quiz 3 - MCQExams.com
CBSE
Class 12 Commerce Applied Mathematics
Probability Distribution And Its Mean And Variance
Quiz 3
If the variance of the random variable
X
is
4
, then the variance of the random variable
5
X
+
10
is
Report Question
0%
100
0%
10
0%
50
0%
25
Explanation
If a random variable
X
is adjusted by multiplying by the value
b
and adding the value
a
, then the variance is affected as follows:
σ
2
a
+
b
X
=
b
2
σ
2
If the variance of the random variable X =
σ
2
=
4
For the random variable
5
X
+
10
,
σ
2
10
+
5
X
=
b
2
σ
2
=
5
2
4
=
100
σ
2
10
+
5
X
=
100
From a lot of 10 items containing 3 defectives, a sample of 4 items is drawn at random without replacement. The expected number of good items is
Report Question
0%
3
0%
2.8
0%
1.2
0%
1.8
Explanation
Probability of good items =
7
/
10
Total number of items drawn =
4
Expected number of good items =
4
∗
7
/
10
=
2.8
If the probability distribution of a random variable x is
X
=
x
1
:
−
2
−
1
0
1
2
3
p
(
X
=
x
1
)
:
0.1
k
0.2
2
k
0.3
k
then the mean of x is
Report Question
0%
0.6
0%
0.8
0%
1.0
0%
0.3
Explanation
3
∑
i
=
−
2
p
i
=
1
0.1
+
k
+
0.2
+
2
k
+
0.3
+
k
=
1
4
k
=
1
−
0.6
=
0.4
k
=
0.1
M
e
a
n
=
3
∑
i
=
−
2
x
i
p
i
=
−
0.2
−
k
+
2
k
+
0.6
+
3
k
=
4
k
+
0.4
=
0.4
+
0.4
=
0.8
The Probability distribution of a random variable
X
is given by
P
(
X
=
x
)
=
0.1
,
0.1
,
0.1
,
0.3
,
0.4
for
(
X
=
x
)
=
4
,
3
,
2
,
1
,
0
. The variance of
X
is
Report Question
0%
1.
76
0%
2.45
0%
3.2
0%
4.8
Explanation
Mean =
∑
x
i
p
i
=
1.24
variance =
∑
(
x
i
−
ˉ
x
)
2
p
i
=
1.44
∗
0.4
+
0.2
2
∗
0.3
+
0.8
2
∗
0.1
+
1.8
2
∗
0.1
+
2.8
2
∗
0.1
=
1.76
If a random variable
x
has the following probability distribution
X
=
x
i
:
0
1
2
3
P
(
X
=
x
i
)
:
2
K
2
,
3
K
2
,
5
K
2
,
6
K
2
then the value of
K
is
Report Question
0%
1
4
0%
−
1
4
0%
±
1
4
0%
1
2
Explanation
Using the fact ,
∑
P
(
X
)
=
1
⇒
2
K
2
+
3
K
2
+
5
K
2
+
6
K
2
=
1
⇒
K
2
=
1
16
⇒
K
=
±
1
4
The value of
C
for which
P
(
X
=
k
)
=
C
k
2
can serve the probability function of a random variable
X
that takes values
0
,
1
,
2
,
3
,
4
is
Report Question
0%
1
30
0%
1
10
0%
1
3
0%
1
15
Explanation
4
∑
k
=
0
P
(
X
=
k
)
=
1
⇒
4
∑
k
=
0
c
k
2
=
1
⇒
c
(
1
2
+
2
2
+
3
2
+
4
2
)
=
1
⇒
c
=
1
30
If the probability distribution of a random variable
x
is
X
=
x
1
:
−
2
−
1
0
1
2
3
p
(
X
=
x
1
)
:
0.1
k
0.2
2
k
0.3
k
, then the variance of
x
is
Report Question
0%
2.16
0%
2.8
0%
√
2.16
0%
√
2.8
Explanation
3
∑
i
=
−
2
p
i
=
1
0.1
+
k
+
0.2
+
2
k
+
0.3
+
k
=
1
4
k
=
1
−
0.6
=
0.4
k
=
0.1
E
[
X
]
=
3
∑
i
=
−
2
x
i
p
i
=
−
0.2
−
k
+
2
k
+
0.6
+
3
k
=
4
k
+
0.4
=
0.4
+
0.4
=
0.8
E
[
X
2
]
=
3
∑
i
=
−
2
x
2
p
i
=
0.4
+
k
+
2
k
+
1.2
+
9
k
=
2.6
V
a
r
i
a
n
c
e
=
E
[
X
2
]
−
E
[
X
]
2
=
2.6
−
0.8
2
=
2.16
If a random variable
x
has the following probability distribution
X
=
x
i
:
0
1
2
3
P
(
X
=
x
i
)
:
2
K
2
3
K
2
5
K
2
6
K
2
Then find the mean.
Report Question
0%
33
16
0%
31
16
0%
35
16
0%
29
16
Explanation
Using
∑
P
(
X
)
=
1
⇒
16
K
2
=
1
⇒
K
2
=
1
16
Thus mean
=
∑
x
i
P
(
X
=
x
i
)
=
0
+
P
(
X
=
1
)
+
2
P
(
X
=
2
)
+
3
P
(
X
=
3
)
0
+
3
K
2
+
10
K
2
+
18
K
2
=
31
K
2
=
31
16
The probability distribution of a random variable
X
is given below, then
K
=
X
=
x
1
:
1
,
2
,
3
,
4
p
(
X
=
x
1
)
:
2
k
,
4
k
,
3
k
,
k
Report Question
0%
1
4
0%
1
5
0%
1
10
0%
1
15
Explanation
4
∑
1
P
(
X
=
x
)
=
1
K
(
2
+
4
+
3
+
1
)
=
1
K
=
1
10
A random variable
X
takes the values
−
1
,
0
,
+
1
. Its mean is
0.6
. If
P
(
X
=
0
)
=
0.2
, then find
P
(
X
=
1
)
and
P
(
X
=
−
1
)
Report Question
0%
0.2
,
0.8
0%
0.3
,
0.7
0%
0.7
,
0.1
0%
0.4
,
0.2
Explanation
We know
∑
P
(
X
)
=
1
⇒
P
(
X
=
−
1
)
+
P
(
X
=
0
)
+
P
(
X
=
1
)
=
1
⇒
P
(
X
=
−
1
)
+
P
(
X
=
1
)
=
0.8
-----(i)
Given mean is
10.6
⇒
(
−
1
)
(
P
(
X
=
−
1
)
)
+
(
0
)
(
P
(
X
=
0
)
)
+
1
(
P
(
X
=
1
)
)
=
0.6
⇒
−
P
(
X
=
−
1
)
+
P
(
X
=
1
)
=
0.6
------(ii)
Adding (i) and (ii)
2
P
(
x
=
1
)
=
1.4
P
(
x
=
1
)
=
0.7
P
(
x
=
−
1
)
=
0.8
−
P
(
x
=
1
)
=
0.8
−
0.7
=
0.1
∴
P
(
X
=
−
1
)
=
0.1
,
P
(
X
=
1
)
=
0.7
The value of k, if the probability distribution of a
X
=
x
:
1
,
2
,
3
random variable X is
p
(
X
=
x
)
:
1
k
,
2
k
,
3
k
is
Report Question
0%
1
6
0%
6
0%
1
3
0%
1
√
6
Explanation
concept : {
sum of probability distribution against random variable always is equal to 1 }
n
∑
i
=
1
P
(
x
i
)
=
1
1
k
+
2
k
+
3
k
=
1
6
k
=
1
k
=
6
value of k is 6.
A random variable
X
has the following probability distribution, then
C
=
X
=
x
:
1
,
2
,
3
,
4
,
P
(
X
=
x
)
:
C
,
2
C
,
3
C
,
4
C
Report Question
0%
0.1
0%
0.2
0%
10
0%
20
Explanation
4
∑
1
P
(
X
=
x
)
=
1
C
(
2
+
4
+
3
+
1
)
=
1
C
=
0.1
A random variable
X
takes the values
0
,
1
,
2
,
3
and its mean is
1.3
. If
P
(
X
=
3
)
=
2
P
(
X
=
1
)
and
P
(
X
=
2
)
=
0.3
, then
P
(
X
=
0
)
=
Report Question
0%
0.1
0%
0.2
0%
0.3
0%
0.4
Explanation
E
[
X
]
=
3
∑
i
=
0
x
i
p
i
=
0
∗
P
(
X
=
0
)
+
1
∗
P
(
X
=
1
)
+
2
∗
P
(
X
=
2
)
+
3
∗
P
(
X
=
3
)
=
1.3
1
∗
P
(
X
=
1
)
+
2
∗
0.3
+
3
∗
2
∗
P
(
X
=
1
)
=
1.3
P
(
X
=
1
)
=
0.1
N
o
w
u
s
i
n
g
3
∑
i
=
0
p
i
=
1
=
P
(
X
=
0
)
+
P
(
X
=
1
)
+
P
(
X
=
2
)
+
P
(
X
=
3
)
P
(
X
=
0
)
+
0.1
+
0.3
+
0.2
=
1
P
(
X
=
0
)
=
0.4
The variance of the random variable
x
whose probability distribution is given by
X
=
x
:
0
1
2
3
p
(
X
=
x
)
:
1
3
1
2
0
1
6
Report Question
0%
0.5
0%
1
0%
1.5
0%
2.0
Explanation
E
[
X
]
=
3
∑
i
=
0
x
i
p
i
=
0
+
1
2
+
0
+
1
2
=
1
E
[
X
2
]
=
3
∑
i
=
0
x
2
p
i
=
0
+
1
2
+
0
+
9
6
=
2
V
a
r
i
a
n
c
e
=
E
[
X
2
]
−
E
[
X
]
2
=
2
−
1
2
=
1
If
X
is a random variable with the following probability distribution given below:
X
=
x
0
1
2
3
P
(
X
=
x
)
k
3
k
3
k
k
Then the value of
k
and its variance are:
Report Question
0%
1
8
,
22
27
0%
1
8
,
23
27
0%
1
8
,
8
9
0%
1
8
,
3
4
Explanation
3
∑
i
=
−
2
p
i
=
1
k
+
3
k
+
3
k
+
k
=
1
⇒
k
=
1
8
E
[
X
]
=
3
∑
i
=
0
x
i
p
i
=
0
×
P
(
X
=
0
)
+
1
×
P
(
X
=
1
)
+
2
×
P
(
X
=
2
)
+
3
×
P
(
X
=
3
)
3
k
+
6
k
+
3
k
=
12
k
=
12
8
E
[
X
2
]
=
3
∑
i
=
0
x
2
p
i
=
3
k
+
12
k
+
9
k
=
24
k
=
3
V
a
r
i
a
n
c
e
=
E
[
X
2
]
−
E
[
X
]
2
=
3
−
(
3
2
)
2
=
3
−
9
4
=
3
4
A random variable X follows the following distribution
X
=
x
i
:
1
,
2
,
3
,
4
p
(
X
=
x
i
)
:
2
6
,
3
6
,
0
6
,
1
6
, then the mean and variance are
Report Question
0%
1
,
1
0%
1
,
2
0%
2
,
1
0%
2
,
2
Explanation
E
[
X
]
=
4
∑
i
=
1
x
i
p
i
=
1
∗
P
(
X
=
1
)
+
2
∗
P
(
X
=
2
)
+
3
∗
P
(
X
=
3
)
+
4
∗
P
(
X
=
4
)
=
2
6
+
6
6
+
0
6
+
4
6
=
2
E
[
X
2
]
=
3
∑
i
=
0
x
2
p
i
=
2
6
+
12
6
+
0
6
+
16
6
=
5
V
a
r
i
a
n
c
e
=
E
[
X
2
]
−
E
[
X
]
2
=
5
−
2
2
=
1
A random variable X has its range
1
,
2
,
3
with respective probabilities
P
(
X
=
1
)
=
K
,
P
(
X
=
2
)
=
2
K
,
P
(
X
=
3
)
=
3
K
,
then the value of K is
Report Question
0%
1
4
0%
1
5
0%
1
6
0%
1
8
Explanation
3
∑
1
P
(
X
=
x
)
=
1
K
(
1
+
2
+
3
)
=
1
K
=
1
6
Let X be the random variable with the probability distribution function
f
(
x
)
=
e
−
4
4
x
x
!
;
x
=
0
,
1
,
2
,
3
,
.
.
.
.
then the standard deviation of X is
Report Question
0%
2
0%
4
0%
16
0%
√
2
Explanation
The above distribution is Poisson Distribution of type
P
(
k
)
=
e
−
λ
.
λ
k
k
!
Here
λ
=
4
.
Now
M
e
a
n
=
V
a
r
i
a
n
c
e
=
λ
in a Poisson Distribution.
Hence
V
a
r
i
a
n
c
e
=
λ
=
4
Or
S
.
D
2
=
V
a
r
i
a
n
c
e
=
4
Or
S
.
D
=
√
V
a
r
i
a
n
c
e
=
√
4
=
2
.
A random variable
X
has its range
X
=
0
,
1
,
2
with respective probabilities
P
(
X
=
0
)
=
3
K
3
,
P
(
X
=
1
)
=
4
K
−
10
K
2
,
P
(
X
=
2
)
=
5
K
−
1
, then the value of
K
is
Report Question
0%
2
0%
1
0%
1
3
0%
2
,
1
,
1
3
Explanation
Given,
P
(
X
=
0
)
=
3
K
3
,
P
(
X
=
1
)
=
4
K
−
10
K
2
,
P
(
X
=
2
)
=
5
K
−
1
Now,
P
(
X
=
0
)
+
P
(
X
=
1
)
+
P
(
X
=
2
)
=
1
⇒
3
K
3
−
10
K
2
+
9
K
−
2
=
0
⇒
(
K
−
1
)
(
3
K
2
−
7
K
+
2
)
=
0
⇒
(
K
−
1
)
(
K
−
2
)
(
3
K
−
1
)
=
0
⇒
K
=
1
,
2
,
1
3
But
K
=
1
,
2
not possible as at these values of
K
, the probabilities
P
(
X
=
0
)
,
P
(
X
=
1
)
,
P
(
X
=
2
)
does not lie between
0
and
1
.
If a random variable X takes values
(
−
1
)
k
2
k
/
k
;
k
=
1
,
2
,
3
,
.
.
.
.
with probabilities
P
(
X
=
k
)
=
1
2
k
then E(X)=
Report Question
0%
l
o
g
2
0%
l
o
g
e
0%
l
o
g
(
1
2
)
0%
l
o
g
(
1
4
)
Explanation
E
[
X
]
=
∞
∑
k
=
1
(
−
1
)
k
2
k
k
1
2
k
=
(
−
1
)
k
k
=
−
1
1
+
1
2
+
−
1
3
+
1
4
+
.
.
.
.
.
.
.
.
=
−
1
+
1
2
−
1
3
+
1
4
+
.
.
.
.
.
.
.
.
.
=
−
log
2
=
log
1
2
If F(x) is the cumulative distributive function of a random variable x whose range is from
−
α
to
+
α
, then
P
(
X
<
−
α
)
Report Question
0%
1
0%
1
2
0%
0
0%
1
3
Explanation
We have for a random variable
X
,
F
(
x
)
=
P
(
X
≤
x
)
=
0
for
x
<
0
(since the random variable cannot assume negative values, so its probability is 0)
So,
P
(
X
<
−
α
)
=
0
A random variable
X
takes value
0
,
1
,
2
. Its mean is
1.3
. If
P
(
X
=
0
)
=
0.2
, then
P
(
X
=
2
)
=
Report Question
0%
0.3
0%
0.4
0%
0.5
0%
0.2
Explanation
Given Mean
=
1.3
,
P
(
x
=
0
)
=
0.2
0
×
P
(
X
=
0
)
+
1
×
P
(
X
=
1
)
+
2
×
P
(
X
=
2
)
=
1.3
Let
P
(
X
=
2
)
=
p
P
(
X
=
1
)
=
1
−
P
(
X
=
0
)
−
p
=
0.8
−
p
Substituting in original equation
P
(
X
=
1
)
+
2
P
(
X
=
2
)
=
1.3
0.8
−
p
+
2
p
=
1.3
p
=
0.5
Let the discrete random variable
X
=
x
has the probabilities given by
x
6
for
x
=
0
,
1
,
2
,
3
, then its mean is
Report Question
0%
1
3
0%
5
3
0%
7
3
0%
9
3
Explanation
E
[
X
]
=
3
∑
i
=
0
x
i
p
i
=
0
∗
P
(
X
=
0
)
+
1
∗
P
(
X
=
1
)
+
2
∗
P
(
X
=
2
)
+
3
∗
P
(
X
=
3
)
=
0
+
1
6
+
2
∗
2
6
+
3
∗
3
6
=
14
6
If the range of the random variable
X
is from
−
α
to
+
α
, the limits of
F
(
X
)
are
Report Question
0%
0
to
α
0%
−
α
to
3
0%
−
1
to
+
1
0%
0
to
1
Explanation
We have for a random variable
X
,
F
(
x
)
=
P
(
X
≤
x
)
=
0
for
x
<
0
(since the random variable cannot assume negative values, so its probability is 0)
F
(
x
)
=
P
(
X
≤
x
)
for
x
≥
0
Since, the value of probability lies between 0 and 1.
So,
0
<
F
(
x
)
≤
1
Hence, limits of
F
(
x
)
are 0 to 1.
The range of a random variable
X
is
1
,
2
,
3
,
4
.
.
.
.
and the probabilities are given by
p
(
X
=
k
)
=
c
k
k
!
k
=
1
,
2
,
3
,
4....
,
, then the value of
C
is
Report Question
0%
2
2
0%
log
e
0%
log
e
2
0%
4
Explanation
We know,
∑
P
(
X
)
=
1
⇒
c
+
c
2
2
!
+
c
3
3
!
+
.
.
.
.
.
.
.
.
.
.
.
=
1
⇒
1
+
c
+
c
2
2
!
+
c
3
3
!
+
.
.
.
.
.
.
.
.
.
.
.
=
1
+
1
=
2
⇒
e
c
=
2
⇒
c
=
log
e
2
A person who tosses an unbiased coin gains two points for turning up a head and loses one point for a tail. If three coins are tossed and the total score
X
is observed, then the range of
X
is
Report Question
0%
0
,
3
,
6
0%
−
3
,
0
,
3
0%
−
3
,
0
,
3
,
6
0%
−
3
,
3
,
6
Explanation
3
coins are tossed . There can be
4
possible outcomes
1.
3
T
,
0
H
. Score
=
−
3
2.
2
T
,
1
H
. Score
=
−
2
+
2
=
0
3.
1
T
,
2
H
. Score
=
−
1
+
4
=
3
4.
0
T
,
3
H
. Score
=
0
+
6
=
6
Hence, the range of
X
is
{
−
3
,
0
,
3
,
6
}
A discrete random variable
X
, can take all possible integer values from
1
to
K
, each with a probability
1
/
K
. Its mean is
Report Question
0%
K
0%
K
+
1
0%
K
/
2
0%
K
/
4
Explanation
Mean
=
μ
=
K
∑
i
=
1
x
i
p
i
=
1
×
1
+
2
×
1
2
+
3
×
1
3
+
.
.
.
.
.
K
×
1
K
=
1
+
1
+
.
.
.
.
u
p
t
o
K
t
i
m
e
s
Mean
μ
=
K
In a World Cup final match against Srilanka, for six times Sachin Tendulkar hits a six out of 30 balls he plays. What is the probability that in a given throw, the ball does not hit a six?
Report Question
0%
1
4
0%
5
4
0%
4
5
0%
3
4
The probability distribution of random variable X: number of heads , when a fair coin is tossed twice is given by
x
0
1
2
p(x)
p
1
p
2
p
3
then
Report Question
0%
∑
p
i
=
0
0%
Π
p
i
=
1
0%
∑
p
i
=
1
0%
∑
p
i
=
3
Explanation
We know that, the probability distribution of a random variable is a list of probabilities associated with each of its possible values.
Suppose a random variable
X
may take
k
different values, with the probability that
X
=
x
i
defined to be
P
(
X
=
x
i
)
=
p
i
.
The probabilities
p
i
must satisfy the following:
0
≤
p
i
≤
1
for each
i
p
1
+
p
2
+
.
.
.
+
p
k
=
1.
T
h
a
t
i
s
∑
p
i
=
1
Thus if the probability distribution of random variable
X
: number of heads , when a fair coin is tossed twice is given then
∑
p
i
=
1
A car hire firm has
2
cars which it hires out day by day. If the number of demands for a car on each day follows poisson distribution with parameter
1.5
, then the probability that some demand is refused is
Report Question
0%
1.12
×
e
−
1.5
0%
1.2.5
×
e
−
1.5
0%
1
−
3.625
×
e
−
1.5
0%
3.625
×
e
−
1.5
Explanation
let
X
be a random variable denoting the number of demands for a car on any day.
So,
X
is Poisson distributed with the parameter
μ
=
1.5
Therefore, the probability mass function is
P
(
X
=
i
)
=
e
μ
μ
t
i
!
=
e
−
1.5
(
1.5
)
2
i
!
;
i
=
0
,
1
,
2
Now, the proportion of days in which neither car is used is actually the probability of there being no demand of cars which is given by
P
(
X
=
0
)
=
e
−
1.5
(
1.5
)
2
0
!
=
e
−
1.5
and the proportion of days on which some demand is refused, is the probability that the number of demands become more than
2
and is given by
P
(
X
>
2
)
=
1
−
P
(
X
≤
2
)
=
1
−
P
(
X
=
0
)
+
P
(
X
=
1
)
+
P
(
X
=
2
)
=
1
−
e
1.5
(
1.5
)
0
0
!
+
e
−
1.5
(
1.5
)
1
1
!
+
e
−
1.5
(
1.5
)
2
2
!
=
1
−
3.625
×
e
−
1.5
0:0:2
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Practice Class 12 Commerce Applied Mathematics Quiz Questions and Answers
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