Skill: Find probabilities from coloured objects

When all objects are equally likely to be chosen, use:

$$\text{Probability}=\frac{\text{number of objects of the colour}}{\text{total number of objects}}$$

Example: A bag contains 5 red counters, 3 blue counters, and 2 green counters. What is the probability of choosing a blue counter?

1. Count the blue counters.
   There are $3$ blue counters.

2. Find the total number of counters.

$$5+3+2=10$$

3. Write the probability as a fraction.

$$P(\text{blue})=\frac{3}{10}$$

4. Convert if needed.
   The fraction $\frac{3}{10}$ is equal to $(0.3)$, or $(30\%)$.

So, the probability of choosing a blue counter is:

$$\boxed{\frac{3}{10}=0.3=30\%}$$

Only count the objects with the colour you want in the numerator. Count all the objects in the denominator.