# Discrete random variable – distribution of X

• October 24th 2008, 12:45 AM
geton
Discrete random variable – distribution of X
A spinner is made from the disc is the diagram and the random variable X represents the number it lands on after being spun.

http://www.mathhelpforum.com/math-he...1&d=1224834262

Write down the distribution of X.

How could I do this? Basically I’m confused where to start & what to think. Could anyone explain please?
• October 24th 2008, 04:44 AM
Plato
This problem represents a simple idea.
Just find out what percent of the total area each of the sectors represents.
For example, sector 2 is one fourth of the total area.
• October 24th 2008, 08:44 AM
geton
Quote:

Originally Posted by Plato
This problem represents a simple idea.
Just find out what percent of the total area each of the sectors represents.
For example, sector 2 is one fourth of the total area.

So remaining area is 1-1/4 = 3/4.
So sector 1 is 3/4 divided by 2 = 3/8.

Is it like that?
• October 24th 2008, 09:18 AM
Plato
Quote:

Originally Posted by geton
So remaining area is 1-1/4 = 3/4.
So sector 1 is 3/4 divided by 2 = 3/8.

No! Look at the size of the central angles.
Sector 1 is $\frac {125}{360}$ of the total. Sector 3 is $\frac {145}{360}$ of the total.
• October 24th 2008, 09:50 AM
geton
Well my book's answer says for sector 1, 3/8 and sector 3, 3/8. How this 3/8 come?
• October 24th 2008, 10:00 AM
Plato
Quote:

Originally Posted by geton
Well my book's answer says for sector 1, 3/8 and sector 3, 3/8. How this 3/8 come?

Well inorder for those answers to be correct the second number in the diagram would have to be $225^o$ not $215^o$.
So the diagram in incorrect.
• October 24th 2008, 10:14 AM
geton
Quote:

Originally Posted by Plato
Well inorder for those answers to be correct the second number in the diagram would have to be $225^o$ not $215^o$.
So the diagram in incorrect.

It's not my fault. I think it's a printing mistake of my book. Anyways, thank you so much.