Question 321770
A carnival worker is tempting to play his game. 
He has a secret box which contains twenty $1 bills, ten $5 bills, and five $10 bills. 
You can draw one bill out per game; however, the cost of the game is $5. 
Fill in the table for the profit you might win
Gain x:...........-4........0.........5
Probability P(x)..20/35....10/35.....5/35 
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Profit = [20*-4+10*0 + 5*5]/35 = [-80+25]/35 = -55/35 = -11/7 = -$1.57
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Question: where did the 35 value come from?  
The 35 is the common denominator for each of the P(x) factors.
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it also asks what is the expected value of the game?  
The expected profit is a loss of $1.57.
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Cheers,
Stan H.