Question

there are four nickels and six dimes in your pocket. you randomly pick a coin out of your pocket and place it on a counter. then you randomly pick another coin. both are nickels. what is the probability?

Answer 1

2/15.

Explanation:

Probability of the first pick being a nickel = 4/10 = 2/5.

Probability of the second being a nickel = 3/9 = 1/3.

So the probability of 2 nickels = 2/5 * 1/3 = 2/15.

Note: the probabilities are multiplied as the 2 events are independent.

Answer 2

-- When you start out, there are 10 coins in your pocket, and 4 of them are nickels.

If you reach in and pick one coin, with mittens on (so you can't feel which one you're grabbing), your chance of picking a nickel is 4/10 .

-- Then there are 9 coins left in your pocket, and 3 of them are nickels.

-- NOW if you reach in and pick another coin, the chance of picking a nickel is 3/9 .

-- The probability of BOTH events is

P = (4/10) x (3/9)

P = 12/90

P = 13.33 %