Question

There is a bag filled with 4 blue and 5 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 blues

Answer 1

There are total 9 marbles, out of which there are 4 blue and 5 red marbles.

Probability of getting blue marbles in first turn will be $(4/9)$ .

Now, since the ball is replaced, the probability of again getting the blue ball will be same equal to $(4/9)$

Now, from the multiplication theorem of probability, the probability of getting 2 blue balls will be:

$(4/9)*(4/9)=(16/81)$