Question

finding pdf from cdf

Answer 1

Differentiate.

Answer 2

I have cdf F(x)=(\[1+e ^{-x})^{-1}, -\infty<x<\infty\]

Answer 3

and set it to 0?

Answer 4

how i know the intervals though?

Answer 5

The intervals generally do not matter unless you have a very strange piece-wise function.

Answer 6

Even then, I think you'd still differentiate.

Answer 7

The intervals remain the same.

Answer 8

how should i graph the 25th percentile then?

Answer 9

\[
F(x) = \int_{-\infty}^xp(x')dx'
\]

Answer 10

If you differentiate you get: \[
F'(x) = p(x)
\]Which means: \[
p(x) = F'(x)
\]

Answer 11

I don't know what you mean by 25 percentile.

Answer 12

i am suppose to graph the f(x) and F(x) and find 25th percentile

Answer 13

The 25 percentile would be \(F(x)=0.25=1/4\).

Answer 14

ooo okay so for the pdf just differentiate and leave the interval alone

Answer 15

All the intervals remain the same, basically.

Answer 16

It's a bit more complicated for discrete functions. The continuous functions are easy.

Answer 17

okay thanks a lot