Question

Nanette has 5 dimes and 5 pennies in her
pocket. What's the probability that Nanette
pulls out a dime and then a penny from
her pocket? (Assume that she doesn't put
the first dime back in her pocket.)

Answer 1

Answer:

2/9

Step-by-step explanation:

5 dimes and 5 pennies = 10 coins

P( dime) = number of dimes / total

            =5/10 = 1/2

keep the dime

4 dimes and 5 pennies = 9 coins

P( penny) = number of penny / total

                 =4/9

P( dime, keep, penny) = 1/2 * 4/9 = 2/9

Answer 2

Answer:  5/18

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Explanation:

There are 5+5 = 10 coins total, of which 5 are dimes. The probability of selecting a dime is 5/10 = 1/2.

The coin is not put back, so we have 10-1 = 9 coins overall. Of this, 5 are pennies. The probability of pulling a penny out is 5/9. Note how this is dependent on the first event above.

From here, multiply the two probabilities

(1/2)*(5/9) = 5/18

The rule used here is

P(A and B) = P(A)*P(B given A)

where A and B are the events "pulling out a dime on the first selection" and "pulling out a penny on the second selection"