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

16/81

Explanation:

Given

• In the bag, there are : 4 blue and 5 red marbles

Probability of blue (1st time)

• P(1) = Total blue / Total marbles
• P(1) = 4 / (4 + 5)
• P(1) = 4/9

Probability of blue (2nd time)

• P(2) = Total blue / Total Marbles
• It states it is replaced hence it is of the same constitution as the beginning
• P(2) = 4/9

Probability of blue (both times)

• P = P(1) x P(2)
• P = 4/9 x 4/9
• P = 16/81