Stats doubt

[The Villain]

For a random variable X,if E(X)=10 and var(X)=15 then P(5<X<15)is
a <2/5
b >2/5
c <1/3
D NONE OF the above

[Akshay Jain]

Is it b??...
m not sure....i used standardization of variable....(X-10)/underoot 15

[The Villain]

I dont have the ans Akshay. Could you explain your approach?

[Akshay Jain]

Convert the variable into a standarzed varaible with mean 0 and var 1
just like i have done....
the prob that value of this variable lies within 1 s.d. Of mean is approx 68% which is greater dan 2/5
(m not sure about this approach)

[The Villain]

Thanks Akshay.I tried in the same way.Bt i didnt get hw u got within 1 sd??

[Akshay Jain]

P(5<X<15)=P((5-10)/underoot15 < (X-10)/underoot15 < (15-10)/underoot15)
= P(-5/underoot15 < (X-10)/underoot15 < 5/underoot15)
actually its more dan 1 s.d. But it vil not change the answer

[don123]

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[don123]

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[Homer Simpson]

Ron, its (b). this is how i solved.

[Akshay Jain]

At the 1st look i also thot of applying chebishev's rule but I thot dat u pple dont no chebishev's rule....
 u know dats gud infact....

[Akshay Jain]

U pple are from stats or maths pr engineering background kya..??
coz i dont think dat this rule is taught in undergrad economics

[The Villain]

Thanxx a lot guys...Akshay,khiladi,tsuki :)

[Anjali]

Tsuki in which chap in SC Gupta can I find Cheby inequality ?
Iam not clear with its concept.
@ Akshay , in SC Gupta , is linear regression chapter imp ? Also what about joint probability ?

[Anjali]

Tsuki how did you solve the last three steps ? Iam not able to break it into less and greater than forms.

[The Villain]

@Anjali..U have to do joint prob...its imp!
For regression ...refer gujrati..

[Anjali]

Joint and marginal both ?
And , did you understand what has done in the last 3 steps ?

[Anjali]

In context of our syllabus , what all does come under linear algebra ?

[Homer Simpson]

Check out page 3.36 (its in the dispersion chapter) Linear regression and joint probability must be done

As for the last 3 steps, i simply put the value of the probability i found and sign will change for the expression- because that probability is more than equal to something.

suppose 1 - k is there. if k is less than equal to 1/2, that means k can be 1/2 or something lower, like 1/4
say, (1 - 1/4) = 3/4 or take any smaller k, (1 - k) gets larger

so 1 - k must be atleast 1/2 or bigger...