Lesson 14: Problems About Parts of a Whole, Simple Probability

New Concept

Probability is the likelihood that a particular event will occur. We find the probability of an event using this formula:

What’s next

Next, you'll see this formula in action. We'll solve problems with number cubes and spinners, and explore the concept of complementary events.

Property

Problems about parts of a whole have an addition thought pattern.

Examples

If $\frac{2}{5}$ of students went to the museum, the fraction who did not go is $\frac{5}{5} - \frac{2}{5} = \frac{3}{5}$.
If a phone battery is 82% charged, the percent that is not charged is $100\% - 82\% = 18\%$.
If a team won 9 out of 15 games, the part they did not win is $15 - 9 = 6$ games.

Explanation

Think of a whole pie! If you know the size of one slice, you can figure out what's left. Just subtract the part you know from the whole (which is 1 or 100%) to find the unknown part. Easy as pie!

Property

Probability is the likelihood that a particular event will occur.

Examples

A bag has 2 red and 8 green marbles. The probability of picking red is $\operatorname{P}(\text{Red}) = \frac{2}{10} = \frac{1}{5}$.
When rolling a six-sided die, the probability of rolling a 3 is $\operatorname{P}(3) = \frac{1}{6}$.
When rolling a six-sided die, the probability of rolling an even number (2, 4, 6) is $\operatorname{P}(\text{Even}) = \frac{3}{6} = \frac{1}{2}$.

Explanation

Probability tells you the chance of something happening. It's a simple fraction: divide the number of ways your desired event can occur by the total number of possible outcomes. This gives you a value from 0 (impossible) to 1 (certain)!