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I have 5 marbles numbered 1 through 5 in a bag. Suppose I take out two different marbles at random. What is the expected value of the sum of the numbers on the marbles? Answer as a decimal to the nearest tenth.

 Nov 14, 2020
 #1
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5C 2  =  10

 

So we have ten possible sums

1 + 2  = 3       2 + 3  = 5      3  + 4  =  7      4 + 5  =  9

1+ 3  =  4       2 + 4  = 6      3 +  5  =  8

1 + 4 =  5       2 + 5 =  7

1 + 5  = 6

 

Expected value  =

 

3 *  Prob of occurence  + 4 * Prob of occurence + 5*Prob of occurence + 6 * Prob of occuence +

7 * Prob of occurence   + 8 * Prob of occurence  + 8 * Prob of occurence

 

3 (1/10)  + 4(1/10) + 5(2/10) + 6(2/10)  + 7 (2/10) + 8 (1/10) + 9(1/10)  =

 

3/10  + 4/10  + 10/10  + 12/10 + 14/10  + 8/10 + 9/10 =  

 

60/10

 

6

 

 

cool cool cool

 Nov 14, 2020

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