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Suppose I have a bag with 12 slips of paper in it. Some of the slips have a 2 on them, and the rest have a 7 on them. If the expected value of the number shown on a slip randomly drawn from the bag is 3.25 , then how many slips have a 2?

 Dec 4, 2021
 #1
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3a  + 18 ==39,      

[3a  +  18] / 12==3.25, solve for a

 

There are: 9 twos  and 3 sevens

 Dec 5, 2021
 #2
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x = number of 2's

12-x  = number of 7's

 

[2 *x   +   7 (12-x)] / 12     = 3.25

 2x -7x    + 84 = 39

-5x = -45

x = 9   

 Dec 5, 2021

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