Outcomes

Tree Diagram

Example 1: Sanwiches

When making a sandwich, you can have either wheat or white bread, and inside you can have either ham or cheese. How many sandwiches can you make?

1.    Let's make a  tree diagram....except it will look different here.

•       Wheat: 1. Ham

                          2. Cheese

•       White: 1. Ham

                          2. Cheese

2.    As you can see, there are four possible sandwiches. In a tree diagram, you list the possibilities: you can have wheat with either ham or cheese, and the same applies for white.

A shortcut: 2 * 2 = 4.

Probability

First, let's be sure we're on the same page here; this is 4th grade probability, not more complex probability like C(32, 12) or 25! or etc. This is simple probability, no independent events or permutation yet.

If you've been needing help with probability thank my little sister for this page ^^

Probability as a Fraction

In fractions, there's a scale you as a student will want to use:

Source: Harcourt Math

This, for now, probably doesn't make much sense to you, so let's go on.

Example 1: Marbles in a Bag

There is a bag containing 1 red marbles, 1 yellow marble, 2 green marbles, and 2 blue marbles. What is the probability you will pull a red marble from the bag? How likely is it?

Here are the steps we will follow:
1.    First we need to count the amount of marbles in the bag. 1 + 1 + 2 + 2 = 6.

2.    Now, how many red marbles are there? 1.

3.    So out of 6 marbles, 1 is red.

   We would write our answer as 1/6, and according to the graph above, is less likely.