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If a random variable XX has the following probability distribution:

X01234
P(X)k2k3k6k²

, then

Match List-I with List-II

List-IList-II
(A) k(I) 3/7
(B) P(X<2)P(X < 2)(II) 6/49
(C) P(X>3)P(X > 3)(III) 1/7
(D) P(2X3)P(2 \leq X \leq 3)(IV) 22/49

Choose the correct answer from the options given below:

Solution

Correct Option: 4

For any probability distribution, the sum of all probabilities must equal 1.

P(X=0)+P(X=1)+P(X=2)+P(X=3)+P(X=4)=1P(X=0) + P(X=1) + P(X=2) + P(X=3) + P(X=4) = 1

k+2k+3k+k2+6k2=1k + 2k + 3k + k^2 + 6k^2 = 1

6k+7k2=16k + 7k^2 = 1

7k2+6k1=07k^2 + 6k - 1 = 0

k=6±364(7)(1)2×7k = \dfrac{-6 \pm \sqrt{36 - 4(7)(-1)}}{2 \times 7}

k=6±6414k = \dfrac{-6 \pm \sqrt{64}}{14}

k=6±814k = \dfrac{-6 \pm 8}{14}

This gives two values:

k=6+814=214=17k = \dfrac{-6 + 8}{14} = \dfrac{2}{14} = \dfrac{1}{7} (valid)

k=6814=1414=1k = \dfrac{-6 - 8}{14} = \dfrac{-14}{14} = -1 (rejected, probability cannot be negative)

Therefore k=17k = \dfrac{1}{7}

(A) matches with (III)


P(X<2)P(X < 2) means XX can be 0 or 1.

P(X<2)=P(X=0)+P(X=1)P(X < 2) = P(X=0) + P(X=1)

P(X<2)=k+2kP(X < 2) = k + 2k

P(X<2)=3kP(X < 2) = 3k

P(X<2)=3×17P(X < 2) = 3 \times \dfrac{1}{7}

P(X<2)=37P(X < 2) = \dfrac{3}{7}

(B) matches with (I)


P(X>3)P(X > 3) means XX can only be 4.

P(X>3)=P(X=4)P(X > 3) = P(X=4)

P(X>3)=6k2P(X > 3) = 6k^2

P(X>3)=6×(17)2P(X > 3) = 6 \times \left(\dfrac{1}{7}\right)^2

P(X>3)=6×149P(X > 3) = 6 \times \dfrac{1}{49}

P(X>3)=649P(X > 3) = \dfrac{6}{49}

(C) matches with (II)


P(2X3)P(2 \leq X \leq 3) means XX can be 2 or 3.

P(2X3)=P(X=2)+P(X=3)P(2 \leq X \leq 3) = P(X=2) + P(X=3)

P(2X3)=3k+k2P(2 \leq X \leq 3) = 3k + k^2

P(2X3)=3(17)+(17)2P(2 \leq X \leq 3) = 3\left(\dfrac{1}{7}\right) + \left(\dfrac{1}{7}\right)^2

P(2X3)=37+149P(2 \leq X \leq 3) = \dfrac{3}{7} + \dfrac{1}{49}

P(2X3)=2149+149P(2 \leq X \leq 3) = \dfrac{21}{49} + \dfrac{1}{49}

P(2X3)=2249P(2 \leq X \leq 3) = \dfrac{22}{49}

(D) matches with (IV)


The correct matching is:

(A) k → (III) 17\dfrac{1}{7}

(B) P(X<2)P(X < 2) → (I) 37\dfrac{3}{7}

(C) P(X>3)P(X > 3) → (II) 649\dfrac{6}{49}

(D) P(2X3)P(2 \leq X \leq 3) → (IV) 2249\dfrac{22}{49}

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