Please help :( statistice

The discrete random variable X has the probability function shown below.

x 1 2 3 4 5
P(X=x) a 0.15 0.1 0.25 b

For this distribution E(X)=3.3

A)Show that a=0.2 and b=0.3
B)find P(X 'IS LESS THAN OR EQUAL TO' 2)
C)Find E(3X-1)
D) Find Var(x)

I WOULD BE SOE GRATEFUL FOR SOME HELP. IM NOT LOOKING FOR ANSWERS...JUST SOME GUIDANCE IN HOW TO ANSWER.. PLS

417459n said:

The discrete random variable X has the probability function shown below.
x 1 2 3 4 5
P(X=x) a 0.15 0.1 0.25 b
For this distribution E(X)=3.3
A)Show that a=0.2 and b=0.3
B)find P(X 'IS LESS THAN OR EQUAL TO' 2)
C)Find E(3X-1)
D) Find Var(x)

Click to expand...

You should always post some of your own work!
We know that \(\displaystyle a+(,15)+(.1)+(.25)+b=1 \) and \(\displaystyle (1)a+(2)(,15)+(3)(.1)+(4)(.25)+(5)b=3.3 \)

Now you have two equations in two variables. Proceed.

pka said:

You should always post some of your own work!
We know that \(\displaystyle a+(,15)+(.1)+(.25)+b=1 \) and \(\displaystyle (1)a+(2)(,15)+(3)(.1)+(4)(.25)+(5)b=3.3 \)

Now you have two equations in two variables. Proceed.

Click to expand...

Thankyou.

for part b i got 0.35
for part c i got E(3X-1) = 3E(x)-1
3 * 3.3 -1=8.9?
for part d i got that the var(X) is 2.31?