a bag contains 13 marbles of which 10 are red. A marble is selected at random and replaced. A second marble is then selected at random. What is the probability that both marbles are red?

can some one please help me

The prob of red for the first marble is 10/13

since you are returning it, the second try has the same probability
so ...
(10/13)(10/13) = 100/169

Thank you Reiny so then when ever they are asking something similar like this question I always mult. then? or it depends on what the question is asking me for.

Joe

To find the probability that both marbles selected are red, you will need to calculate the probability of selecting a red marble on the first draw and then the probability of selecting another red marble on the second draw.

Step 1: Calculate the probability of selecting a red marble on the first draw:
Since there are 10 red marbles out of a total of 13 marbles, the probability of selecting a red marble on the first draw is 10/13.

Step 2: Calculate the probability of selecting a red marble on the second draw:
After replacing the first marble, the total number of marbles remains the same, so there are still 10 red marbles out of 13. Therefore, the probability of selecting another red marble on the second draw is also 10/13.

Step 3: Multiply the probabilities:
To find the probability of both events happening, multiply the probability of the first draw (10/13) by the probability of the second draw (10/13):
(10/13) * (10/13) = 100/169 = 0.5917

So, the probability of both marbles being red is approximately 0.5917 or 59.17%.