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)=1
k+2k+3k+k2+6k2=1
6k+7k2=1
7k2+6k−1=0
k=2×7−6±36−4(7)(−1)
k=14−6±64
k=14−6±8
This gives two values:
k=14−6+8=142=71 (valid)
k=14−6−8=14−14=−1 (rejected, probability cannot be negative)
Therefore k=71
(A) matches with (III)
P(X<2) means X can be 0 or 1.
P(X<2)=P(X=0)+P(X=1)
P(X<2)=k+2k
P(X<2)=3k
P(X<2)=3×71
P(X<2)=73
(B) matches with (I)
P(X>3) means X can only be 4.
P(X>3)=P(X=4)
P(X>3)=6k2
P(X>3)=6×(71)2
P(X>3)=6×491
P(X>3)=496
(C) matches with (II)
P(2≤X≤3) means X can be 2 or 3.
P(2≤X≤3)=P(X=2)+P(X=3)
P(2≤X≤3)=3k+k2
P(2≤X≤3)=3(71)+(71)2
P(2≤X≤3)=73+491
P(2≤X≤3)=4921+491
P(2≤X≤3)=4922
(D) matches with (IV)
The correct matching is:
(A) k → (III) 71
(B) P(X<2) → (I) 73
(C) P(X>3) → (II) 496
(D) P(2≤X≤3) → (IV) 4922