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Suppose we have a bag with 10 slips of paper in it. Eight of these have a 2 on them and the other two have a 4 on them.

How many 4's do we have to add to make the expected value equal to 3?

 Nov 24, 2018
edited by Logic  Nov 24, 2018
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2 * (8/10)   + (4 + x) (2/10)  =  3

 

Where x is the number of additional slips showing "4"

Simplify the above.....and we get

 

8/5  + (4 + x) (1/5)   =  3

 

8/5  + 4/5   +  x /5 =  3

 

12 / 5 + x / 5 =  3      [ multiply through by 5 ]

 

12 +  x   =   15

 

And it's obvious that x =   3

 

 

cool cool cool

 Nov 25, 2018

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