Question

A jar contains four blue marbles and two red marbles. Suppose you choose a

marble at random, and do not replace it. Then you choose a second marble.

Find the probability if one of the marbles you select is blue and the other is red.

Answer 1

There is a 50% chance

Answer 2

First we work out the probability that the first marble we select is blue.

To work this out, we divide the number of blue marbles by the total of marbles in the jar:

There are 4 blue marbles and 6 marbles altogether in the jar

So the probability of choosing a blue marble is:

`(4)/(6)`

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Next we work out the probability of then choosing a red marble.

To work this out , we divide the number of red marble by the total of marbles in the jar:

There are 2 red marbles and there are 5 marbles in total

(remember - we have already taken out one blue marble, so there are only 5 marbles left in the jar)

So the probability of choosing a red marble is:

`(2)/(5)`

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Finally, all we do is multiply the two probabilities together:

`(4)/(6)` ×
`(2)/(5)` =
`(8)/(30)` =
`(4)/(15)`

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Answer

`(4)/(15)` or (0.27 as a decimal)