This post hurts my brain. I’d like to say it’s because I’m a writer, and we’re oh-so-bad at math, and that’s just how we are.

But no one gets away from math — our seventh-grade algebra teachers were right, darn it.

We write about numbers all the time. Journalists report on polls. Finance writers cover interest rates. Copywriters promote discounts. Dr. Seuss wrote that thing about the Grinch’s heart growing three sizes that one day.

Forgetting the basics can make you look silly — or, worse, it could cause you to write something incorrect or misleading.

3 things your editor wants you to know about math

>> Want more insights on writing and editing? Follow @danasitar to keep up on Twitter. (I promise, no more math.)

1. “Percent” does not mean “percentage point”

People sometimes use these interchangeably — but they are not interchangeable.

Percent denotes a portion of the whole — 45%, 27%, etc.

Percentage point denotes a single unit of 100 — two points, 12 points, etc.

Writers often mix them up when talking about a change or difference in percentage, like when interest moves up or down, we compare two politicians’ approval ratings, or a study shows a change in the portion of a population that does something.

Some examples:

• Automatic payments knock your mortgage interest rate from 4.5% to 3.5%, a one percentage point savings (4.5 – 3.5 = 1).

• President Doe’s approval rating is 40%, and challenger Senator Schmo’s is 42%. That’s a two percentage point difference — it might also be useful to say Schmo is leading by five percent.

• The city’s Black population grew from 16% to 18% of the total population — an increase of two percentage points.

2. “Median” is not synonymous with “average”

This is a throwback to that seventh-grade math class — remember learning about means and medians? Their distinct definitions matter in how you write:

• Median: The value in an ordered set that has an equal amount of lesser and greater values.

• Mean or average: The value you get when you add up all the values and divide by the number of data points.

Here’s an example: Say the ages of the five people on your team at work are 23, 24, 35, 42 and 64.

• Median age = 35. (Two values are less than 35, and two are greater.)

• Average age (mean) = 37.6 = (23 + 24 + 35 + 42 + 64) ÷ 5.

Don’t conflate “median” and “average” when you write about those numbers. Are you noting the median age in an area, or the average? The median home value, or the average?

Check reports for the language they use — if they say something elusive, like “typical,” reach out to the source for clarification.

In the dictionary, “average” has a mushier definition that means “regular,” the way we use it in everyday language. But if you’re writing about actual stats or numbers, best to stay away from that usage for clarity.

3. PEMDAS

Another time-traveler, back to Algebra I. The acronym PEMDAS represents the order of operations — or, which part of a complicated math problem you do first:

1. Parentheses.

2. Exponents (the small numbers in superscript that mean you multiply the number by itself that many times).

3. Multiply or Divide.

4. Add or Subtract.

Some people use this mnemonic device to remember it: “Please excuse my dear Aunt Sally.” Not sure what Sally’s deal is, but we’ve been apologizing for this beloved relative for decades, and it seems to work.

I had to run an actual correction once when I figured the surface area of a pizza incorrectly because I forgot about ol’ Aunt Sally and the rest.

Here’s how I screwed up:

You find the area of a pizza — a circle — with this formula: 𝜋r2 or pi (that’s 3.14, etc.) times the radius (the distance across the circle) multiplied by itself.

Assuming the radius is 10 inches:

• I did: 3.14 x 10 = 31.4, then 31.42 = 985.96 square inches. Nope.

• Correct: Exponents first. So: 102 = 100, then 100 x 3.14 = 314 square inches. That’s a way different amount of pizza, and getting this information correct is obviously vital.

Bonus: Exercises

Instead of cramming more information into your brain this month, here are three exercises to help you practice what you learned above (answers at the end):

1. Find the percent change and the percentage point change: 37% to 42%

2. Name the mean (average) and median of this set: 12, 13, 17, 47, 82, 83, 97

3. Use PEMDAS to solve this formula: (4 + 17) x (8 – 5)2 + 7 = ?

Further reading

1. Why Writers Should Learn Math (The New Yorker): Journalist Alexander Nazaryan explains how some of the best creative writers use mathematical principles to create well-structured, rhythmic prose and poetry.

2. Writers Do Need Math (Don’t Panic) (ASJA Confidential): “Math for Grownups” author Laura Laing shows journalists and authors two important ways you’ll use math frequently in your writing career.

3. Math for Journalists: How to present numbers to readers without making their eyes glaze over (Poynter): These four simple tips will help you write about numbers in a way readers can decipher — and maybe even enjoy!

4.Newsroom Math Crib Sheet (National Center for Business Journalism): 🚨Bookmarkable link! Writer Sally Kilbridge lists 11 basic formulas that’ll come in handy when you need to describe anything with numbers.

5. Math basics for journalists: Working with averages and percentages (Journalist’s Resource): Research editor Leighton Walter Kille explains how to figure and write about averages and percentages in more detail. (If you write about data often, follow this site! It’s a fantastic resource.)

Answers — you want ‘em, I’ve got ‘em!

1. Percent change: 13.5%;  Percentage point change: 5

2. Mean: 50; Median: 47

3. ? = 196

Next month

5 types of nonfiction articles your editor wants you to know how to write

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