# Math Help - true???

1. ## true???

the comulative distribution :
given by >>>>
F(x)=
0 x<=0
x\8 0<=x<4
x^2\16 2<=x<4
1 x>=4

find >>>>>>>>>
1-mean of (-2-3x)
2-p(1<x<3)
my solutions
1-mean = -41\4
2- p(1<x<3)= 1\4

2. Originally Posted by flower3
the comulative distribution :

given by >>>>
F(x)=
0 x<=0
x\8 0<=x<4
x^2\16 2<=x<4
1 x>=4

find >>>>>>>>>
1-mean of (-2-3x)
2-p(1<x<3)
my solutions
1-mean = -41\4

2- p(1<x<3)= 1\4
The mean cannot be negative, the probability that $x$ is less than or equal $0$ is $0$.

You need to find the density $f(x)=F'(x)$ (you don't need to worry about this being undefined at a finite number of points) first then the mean will be:

$\int_{-\infty}^{\infty} x f(x)\ dx$

$p(1

RonL

3. the probability impossible equal negative since:

0<=p(x)<=1

but the mean maybe negative or positive>>>>

4. Originally Posted by flower3
the probability impossible equal negative since:

0<=p(x)<=1

but the mean maybe negative or positive>>>>
Look at the definition of mean, if p(x)=0 far all x<0, then the integrand of defining integral for the mean is never negative, so the integral is positive.

If the probability that a rv is negative is zero, the mean is of necessity positive (or zero).

RonL

5. Originally Posted by flower3
the comulative distribution :

given by >>>>
F(x)=
0 x<=0
x\8 0<=x<4 Mr F says: That 4 should be a 2.
x^2\16 2<=x<4
1 x>=4

find >>>>>>>>>
1-mean of (-2-3x)
2-p(1<x<3)
my solutions
1-mean = -41\4

2- p(1<x<3)= 1\4
The hard evidence supporting CaptainB (not that he needs supporting since his comments are bombproof) is that the mean (assuming my correction is correct) is 31/12.

6. yes
mr fantasticyour saying is true(2 not 4)

i think the truth is :

1-mean = -39\4

2- p(1<x<3)= 7\16

7. Originally Posted by CaptainBlack
Look at the definition of mean, if p(x)=0 far all x<0, then the integrand of defining integral for the mean is never negative, so the integral is positive.

If the probability that a rv is negative is zero, the mean is of necessity positive (or zero).

RonL
Ahh.. I see my confusion I was misreading the question you want the mean of $-2-3x$ which is of course negative since the mean of x is positive, and so is equal to $-2-3\bar{x}$

RonL

8. Originally Posted by CaptainBlack
Ahh.. I see my confusion I was misreading the question you want the mean of $-2-3x$ which is of course negative since the mean of x is positive, and so is equal to $-2-3\bar{x}$

RonL
Don't worry