Question

A bag contains 10 marbles, and 4 of the marbles are black. Joseph chooses 2 marbles at random without replacing the first marble. What is the probability that both marbles are black?

Answer 1

2 of the marbles are black

Answer 2

4

Answer 3

not 2

Answer 4

to find the probability that both are black, consider one marble at a time:

for the first draw, there are 4 black marbles out of 10 total, so the probability is 4/10 for the first marble

now, to calculate the second draw, subtract 1 black marble from the total, and re-calculate the probability of drawing another black marble using the same logic

multiply the two probabilities together to get the probability of both draws