A jar contains four blues marbles and two green marbles. Without looking, two marbles are drawn from the jar. What is the probability that two marbles with the same color will be selected?
math - PsyDAG, Friday, August 15, 2014 at 1:15pm
If the events are independent, the probability of both/all events occurring is determined by multiplying the probabilities of the individual events.
For blue = 4/6 * 3/5 = 2/5
For green = 2/6 * 1/5 = 1/10
Either-or probabilities are found by adding the individual probabilities.
2/5 + 1/10 = ?
math - A, Friday, August 15, 2014 at 1:18pm
2/5+1/10 is 5/10.
But in my book it states that the answer is 7/15, without an explanation.
math - Reiny, Friday, August 15, 2014 at 11:29pm
Either two blues or two greens
prob of 2 blues = (4/6)(3/5) = 2/5
prob of 2 grees = (2/6)(1/5) = 1/15 , this is where PsyDAG slipped up
so prob of 2 of same colour = 2/5 + 1/15 = 7/15
math - PsyDAG, Saturday, August 16, 2014 at 1:50pm
⁄Mia Culpa! Sorry.