Question

There is a bag filled with 3 blue and 4 red marbles.

A marble is taken at random from the bag, the colour is noted and then it is replaced.
Another marble is taken at random.
What is the probability of getting 2 that are different in colour?

Answer 1

24/49

Explanation:

The options to get 2 of different color is picking blue then red or red then blue.

Starting with picking blue then red.

The chance to pull blue first is 3/7. Then since the marble is replaced the chance to pull red next is 4/7.

The chance to get those in that specific order is the product of the two fractions. (3/7) * (4/7) = 12 / 49

The second option of getting red then blue will be the same as above but 4/7 then 3/7 with the same result of 12/49.

To finish, add the two probabilities together 12/49 + 12/49 = 24/49.