The probability distribution of a discrete random variable-Finding Fx

Question

The probability distribution of a discrete random variable "X" is given below:

Value x of X: P(X=x)

-5      :  0.24
-4      :  0.16
-3      :  0.17
-2      :  0.15
-1      :  0.28

Let Fx be the cumulative distribution function of . Compute the following:

Fx(-2)=

Fx(-1)-Fx(-4)=

Fx(-16/5)=

My answer

$Fx(-2)= 0.24+0.16+0.17+0.15= 0.72$

$Fx(-1)-Fx(-4)= 0.28+0.15+0.17+0.16= 0.76$

$Fx(-16/5)= 0.24+0.16=0.4$

Is my answer correct?

Answer 1

You are correct that $$Fx(-2) = 0.72$$ I believe $$Fx(-1) - Fx(-4) = [0.24 + 0.16 + 0.17 + 0.15 + 0.28] - [0.24 + 0.16] = 0.17 + 0.15 + 0.28 = 0.60$$ Alternatively we could solve $Fx(-1) - Fx(-4) = 1 - 0.4 = 0.6$.

And you are correct that $$Fx(-16/5) = Fx(-3.2) = 0.24 + 0.16 = 0.4$$ since -3.2 < -3 and we only have probability mass at negative integers.