Question

There is a bag filled with 5 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 of the same colour?

Answer 1

8/18=4/9

Explanation:

since it there is 1/6 for red marbles and 5/18 for blue marbles it works because it is 8*9=72 for the denominator and 4*3=12 so it is 12/72=1/6 and for blue it is 5/18 because it is 5*4=20 and 20/72=10/36=5/18 so it is 1/6+5/18=8/18=4/9