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 not replaced.
Another marble is taken at random.
What is the probability of getting exactly 1 red?

Answer 1

• 5/9

Explanation:

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

If two marbles are taken and we are looking for exactly one red, then it is:

• red, then blue or blue, then red

Find the probability of each case:

• P(r, b) = 5/9*4/8 = 5/18
• P(b, r) = 4/9*5/8 = 5/18

Probability of exactly one red:

• P = 5/18*2 = 5/9