For full tracking and unlimited access to thousands of activities

So far, we have looked at using tree diagrams to find the outcomes of multiple events when we are given the probability of a single event.

Now we need to look at doing this the other way round.

 

Example 1: A bag contains red and blue balls. A ball is picked out, the colour noted and then replaced. This is repeated.

If the probability of picking out two red balls is 1/25. What is the probability of picking out two blue balls.

 

Step 1: Lets put this into a tree diagram.

Step 2: What can we work out?

We know that the probabilities are the same for each event because we are told the ball is replaces.

If we know that P(AA) = 1/25, this is the same as saying P(A) x P(A) = 1.25 so P(A) = 1/5

Step 3: Work out the other event.

We know that A and B are exhaustive, so P(B) must equal 4/5

Step 4: Complete the rest of the tree diagram.

Step 5: Use this to answer the question.

We were initially asked for the Probability of 2 blue balls. From the tree diagram, we can now see that this is 16/25

10 questions