Things You Need to Know
- "Average" can mean one of many things.
- Mean: add all the data values up, divide by the number of data values.
- Median: order the data from least to greatest, pick the middle number.
- If there are two middle numbers, add the numbers and divide by 2.
- Mode: the number that appears the most in a data set (there sometimes is many modes, or sometimes even no mode).
- Weighted mean happens when certain values are worth more than others. The most common use is for school grades.
- To find weighted mean:
- Convert the weightings from percent to decimal.
- Multiply the weightings by the corresponding value.
- Add them all together.
- To find weighted mean:
- An outlier is a number (or numbers) in a data set that are much higher or much lower than the rest.
- Trimmed mean is useful for when we have outliers:
- Remove an outlier.
- If it was a high outlier, remove another number from the low end.
- If it was a low outlier, remove another number from the high end.
- Repeat for all the clear outliers you have.
- Add the remaining numbers together and divide by the amount of remaining numbers.
- Remove an outlier.
- Percentile tells us what percentage of the data is equal to or less than a chosen data value.
- Example: if your height is 60th percentile, then you are as tall or taller than 60% of the population.
- To find percentile, given a data value:
- Order the numbers from least to greatest.
- Count how many places there are (from least to greatest) between the bottom number and your number.
- If your number repeats in the list, count to the highest occurrence of that number.
- Take the place that your number appears in the list and divide by the total number of data values in the list.
- Multiply that answer by 100, and that's your percentile.
- To find a data value, given a percentile.
- Order the numbers from least to greatest.
- Turn the percentile into a decimal by dividing by 100.
- Multiply that by the number of data values in the list.
- Round your answer up, to the next whole number.
- Count that whole number amount from least to greatest in your list.
- The value you get to is your data value.
Interactive Activities
Sample Problems
Class Notes