from a bag containing 2 rupee-coins and 3 twenty paise coins, a person is asked to draw two coins at random. find the values of his expectation.
1 rupee = 100 paise
Therefore, a twenty paise coin is or rupee-coin.
If he draws:
A. 2 rupee-coins, that = 2 rupee
B. 1 rupee-coin and 1 twenty paise coins that = 1.2 rupee
C. 2 twenty paise coins, that = 0.4 rupee
Number of ways to draw A: Draw 2 rupee-coins 1 way
Number of ways to draw B: Draw 1 rupee-coins 2 ways TIMES 3 ways to
draw 1 twenty paise coin. That is 2x3 = 6 ways.
Number of ways to draw C: Draw 2 rupee-coins 3 ways.
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Number of ways to draw ANY 2 coins = 5C2 = 10 ways.
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Probability of A =
Probability of B =
Probability of C =
Draw Value x Probability = Expectation
A 2 x 0.3 .6
B 1.2 x 0.6 .72
C 0.4 x 0.1 .04
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1.0 1.36 rupees
Expectation = 1.36 rupees.
Edwin