past paper q1

[maths_arghh234]

hey my exam next week for statistics, i've got a gew past paper to try. there's a few question i'm stuck on though:\ .. please help !

the random variable X is such that E(X) =5 and var(x) =4 the random variable y is defined by Y=aX-b where a,b are positive constants. given that E(y) =0 and var(y)= 1 find the values of a and b.

what i've done so far...

E(Y) = aE(x) -b
so 5a-b=0

plus var(y) =a^2 var(x)
4a^2 = 1 ....................but dunno what to do next .. :S

 

[tkhunny]

GAAAAaaaaa!!!! Why, I ask you WHY do students forget algebra when they advance to the next class?

Are you SURE you do not know how to solve this system of two variables and two equations?

5a-b = 0
4a^2 = 1

There is a reason why classes are called "prerequisites". You should have learned that material.

 

[Deleted member 4993]

hey my exam next week for statistics, i've got a gew past paper to try. there's a few question i'm stuck on though:\ .. please help !

the random variable X is such that E(X) =5 and var(x) =4 the random variable y is defined by Y=aX-b where a,b are positive constants. given that E(y) =0 and var(y)= 1 find the values of a and b.

what i've done so far...

E(Y) = aE(x) -b
so 5a-b=0

plus var(y) =a^2 var(x)
4a^2 = 1 <<<< If you don't know how to find 'a' from here - you should not be in this class


....................but dunno what to do next .. :S

 

[maths_arghh234]

sorry for the late reply but, i realised the answer thats why i haven't been on here for a while and therefore haven't replied.
-haven't you ever been stuck on a problem and the solution is the obvious one ??
- there aren't any classes calles prerequisites in my school, i'm from UK, i'm assuming your from the USA, obviously the systems are different.
- and ye i probably shouldn't be in this class, i hate being stupid :\

thank you both for replying,

 

[tkhunny]

haven't you ever been stuck on a problem and the solution is the obvious one ??

Wrong question. I did get a question wrong once, and ONLY because I managed to forget something fundamental that I should have remembered and that I first learned years earlier. My professor mocked me openly. He was a great friend. On another occasion, a professor wrote on my exam, "I should fail you for the whole semester for this." He didn't, but I got the point.

- there aren't any classes calles prerequisites in my school, i'm from UK, i'm assuming your from the USA, obviously the systems are different.

That's just not true. Your school system will not let you wander into whatever class you feel like taking. Go try to register for the Advanced Brain Surgery Lab and see what they say. Maybe the word is different, but the concept is not. You must learn what you need before you move on. Milk before meat. It is a universal concept.

- and ye i probably shouldn't be in this class, i hate being stupid

What has it to do with "stupid"? You're just in the wrong class. Back up. Take the prerequisites (whatever you call them), and give it another go.