Question

A bag contains 3 red marbles and 4 blue marbles

one is taken from the bag and replaced
another marble is taken
work out the probability that the two marbles taken from the bag are the same colour
give your answer as a fraction

Answer 1

When a marble is taken out from the bag and replaced, the probability of getting a red or blue marble on the first draw remains the same for the second draw. Therefore, we can use the multiplication rule of probability to calculate the probability of getting two marbles of the same color.

Let's denote the event of getting a red marble as R and the event of getting a blue marble as B. Then, the probability of getting two marbles of the same color can be calculated as follows:

Probability of getting two red marbles: P(R and R) = P(R) * P(R) = (3/7) * (3/7) = 9/49

Probability of getting two blue marbles: P(B and B) = P(B) * P(B) = (4/7) * (4/7) = 16/49

Therefore, the probability of getting two marbles of the same color is the sum of the probabilities of getting two red marbles and two blue marbles, which is:

P(same color) = P(R and R) + P(B and B) = 9/49 + 16/49 = 25/49

So the probability of getting two marbles of the same color is 25/49.

Explanation: