Probability tree diagrams

Probability tree diagrams are the one thing I find my peers always forget.

With a little but of encouragement they could be a master at them! 

Unfortunately, I am a student myself so I do not have the qualifications desired for teaching. But I do know how to teach! 

Lets get into it! 

What does a probability tree diagram look like?

•  Like this.
• You are able to add more ''twigs'' depending on what the question is asking you. 
• The single lines, are were you can write the outcome. 
• This makes probability much easier. 

Lets get right into the questions, and how to do it!

1. Jenny has a bag full of Purple and Blue counters.The chance of pulling out a Purple counter is 3/5. She pulls out two counters, one after the other. What is the chance of pulling out a two blue counters. 

So the first thing we need to look at is the probability of Blue counters. So we know that Purple is 3/5 so Blue must be 2/5.

Now we need a tree diagram!!

Plot what we know!!!

• We have added the fraction amount onto the grid!
• now we need to look at what is left:) 

We know if we take one out of the bag we are left with 4. If we take a Purple out we are left with 2/4 and if we take a Blue out we are left with 1/4. We are able to plot that on the tree now, watch.

• I have filled in the tree diagram, can you see what I did?
• If not, leave a comment and i'll email you to help!:)
• Now we have all our information we can answer the question:)

To be able to find this out we need to be able to multiply fractions. To do that we can times the numerators together and the denominators together. And we are asked to see what is the probability of pulling out two blues.

We now multiply both of the Blue fractions:)

2/5 x 1/4 = 2/20 

We can simplify this 

1/10

and we can turn this into percent = 10% 

With probability you should always answer in % unless is says otherwise :)

Thank you for learning :)