Question

Dwaina draws five marbles out of the original bag of marbles, one at a time. She draws 4 white marbles in a row and then 1 black marble.

Before Dwaina drew each of these marbles, what is the chance she could draw that marble and why?

Answer 1

80%, then 75%, then 66.67%, then 50%, finally 100%

Explanation:

When she first drew a marble there were 5 marbles in the bag: 4 white and 1 black marble. Thus, the chances to pick a white one where 80% since 4 out of the 5 marbles were white.

After picking the first white marble, there are 3 white marbles and 1 black one remaining. the probabilities of picking a white marbel in this case is of 3 in 4, that is the same as 75%.

After picking the second white marble out the bag, there are 2 white marbles and 1 black one remaining. The chances of picking a white one is of 2 in 3, or 66.67%.

After picking the third white marble out the bag only 1 white and 1 black marble remain in the bag. The chances of picking the last white one is 50%.

Finally, only a black marble remains in the bag and the probabilities of picking it is of 100% since there are no other options.