Not What You Expect

I've met so many students over the years who memorized "steps" they to find mean, median, mode and range and then made some serious errors when faced with the data presented in a way they weren't expecting- on a frequency table. Don't be that guy!

LEARN IT:

Be VERY, VERY careful. Frequency tables are a way to organize REPEATED DATA, but students have a very bad habit of ignoring that when trying to compute mean, median, and range. Remember that ALL items must be accounted for when you use the measures of central tendency. There are a few implications of that!

1. You MUST account for repetition when computing the total for the first step of a mean problem. MULTIPLY the frequency times the data item and then add to get the true total of the datas. Be sure you divide by the actual total of the data (ie the total of the frequency column), instead of the number of rows in your table.

2. The median can get REALLY tricky, because the center of the data set is NOT the same as the centermost line of the table. Again, you must account for repetition when finding the centermost item in the data set.

PRACTICE IT:

BEGINNING

MMMR from Frequency Tables- Beginner

EXPERIENCED

Use the Khan Academy Exercises below to practice finding mean and median from data displays, including frequency charts.