1. ## Probability Mass Function

At Fred's Automotive works the arrivals of customes at the Desk is timed.Let X= the number of minutes between successive disgruntled customers. It's found that cumulative distribution function of X is:
F(x)= 0 if x<1
F(x)=0.3 if 1<=x<3
F(x)=0.4 if 3<=x<4
F(x)=0.45 if 4<=x<6
F(x)=0.60 if 6<=x<12
F(x)=1 if 12<=x

What is the pmf of X?
Many thanks to everyone who try to help.

2. Originally Posted by helpmeplease0
At Fred's Automotive works the arrivals of customes at the Desk is timed.Let X= the number of minutes between successive disgruntled customers. It's found that cumulative distribution function of X is:
F(x)= 0 if x<1
F(x)=0.3 if 1<=x<3
F(x)=0.4 if 3<=x<4
F(x)=0.45 if 4<=x<6
F(x)=0.60 if 6<=x<12
F(x)=1 if 12<=x

What is the pmf of X?
Many thanks to everyone who try to help.
I suggest you start by reviewing the relationship between the cdf and pmf of a discrete random variable (I say discrete since your use of the acronym pmf implies this).

Then post what you can do and say where you get stuck.