Skill: Find probabilities from spinners

A spinner’s probability depends on how many equal-sized sections match the event you are looking for.

Use:

$$\text{Probability}=\frac{\text{number of favorable sections}}{\text{total number of sections}}$$

Example

A spinner has $8$ equal sections:

• $3$ red sections
• $2$ blue sections
• $2$ green sections
• $1$ yellow section

What is the probability of landing on blue or green?

Step 1: Count the total sections.

There are $8$ sections altogether, so the sample space has $8$ possible outcomes.

Step 2: Count the favorable sections.

A favorable outcome is landing on blue or green:

$$2+2=4$$

There are $4$ favorable sections.

Step 3: Write the probability as a fraction.

$$P(\text{blue or green})=\frac{4}{8}$$

Step 4: Simplify the fraction and convert if needed.

$$\frac{4}{8}=\frac{1}{2}=0.5=50\%$$

So, the probability of landing on blue or green is:

$$\boxed{\frac{1}{2},\ 0.5,\text{ or }50\%}$$

Remember to combine all sections that match the event. The probability of landing on a color and the probability of not landing on that color add up to $1$, or $100\%$.