Question

Annie’s change purse contained 5 quarters 8 dimes and 8 nickels if Annie chose 2 coin randomly without replacing them in her purse , what is the probability that’s she chose 2 dimes

Answer 1

Answer:

2/15

Explanation:

There are 8C2 = 28 ways to choose 2 dimes from the 8 dimes in Annie's purse. There are 21C2 = 210 ways to choose 2 coins from the 21 coins in Annie's purse.

Of the 210 ways to choose 2 coins, 28 of the choices will result in 2 dimes being chosen. The probability of choosing 2 dimes is 28/210 = 2/15.

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Comment on nCk

The number of ways to choose k objects from n, when order does not matter, is ...

... n!/(k!(n -k)!)

For the computations above, we have ...

... 8C2 = 8·7/(2·1) = 28

... 21C2 = 21·20/(2·1) = 210