Marbles in a bag

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Marbles in a bag

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Marbles

 

Now I'm going to ask you to consider something which may at first seem a bit odd.

 

Imagine that I have a box or a bag filled with thousands of marbles (small balls).

 

Some of the marbles are red. Some are blue.

 

I want to know the proportion of marbles in the bag which are red.

 

There are so many marbles in the bag! I don't have time to count all of them.

 

I decide to reach into the bag (with my eyes closed) and select 20 marbles.

 

This will be a "random sample" of size 20. I might write n=20 to symbolize this.

 

Let's say that 12 of the 20 marbles in my sample are red. I might write x=12

 

So, I picked 20 marbles and 12 were red.

 

12/20 = .6

 

So.

 

I think now about the whole bag, about its "population" of thousands of marbles.

 

I think about my objective: to know the proportion of marbles in the bag which are red.

 

Is the answer .6?