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Can someone help me with this problem for a finite math class.

label Algebra
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A jar contains 3 nickels and 2 dimes. You reach in and randomly select 2 coins. Let x represent the value of the two coins in cents. Find the expected value and standard deviation of x

Mar 10th, 2015

The probability of getting two nickels is (3/5)*(2/4) = 0.3 and the probability of getting two dimes is (2/5)*(1/4) = 0.1. The probability of getting one nickel and one dime is 1 - 0.3 - 0.1 = 0.6.

The expected value is 10*0.3 + 15*0.6 + 20*0.1 = 3 + 9 + 1 = 13 (the combined value of each pair of coins is multiplied by the probability and all the products are added).

The standard deviation is sqrt{(10 - 13)^2 * 0.3 + (15 - 13)^2 * 0.6 + (20 - 13)^2 * 0.1}  = 

sqrt{2.7 + 2.4 + 4.9} = sqrt{10} = 3.16... 

Mar 10th, 2015

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