She Makes Math Fun. Here’s the Proof!

Sue Khim wants you to see the beauty in numbers.

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Master concepts in math and CS


Unlike many people—OK, pretty much everyone—Sue Khim counts among her fondest childhood memories math and long car rides.

As a kid, the cofounder and CEO of the STEM learning app Brilliant was frustrated by the traditional rote memorization methods teachers relied on. Abstract, outside-the-box math challenges appealed to her—especially the ones her father posed. On family road trips, he’d casually fire off questions like “What’s the sum of all the numbers between 1 and 100?”

Brilliant’s multistep approach helps make learning the fundamentals of math more engaging.

“My kid brain starts adding 1 through 10, and I’m quiet for a long time,” Khim recalls. “Then my dad says, ‘Try solving it from the outside in,’ and it became a much easier problem.” (For an explanation of what he meant, see the solution at the end of this story.)

Intrigued by the merging of math and mystery, Khim was hooked. “So much of what I remember about my childhood are these blissful, long car rides,” Khim says. “I learned that a lot of math is about learning a new way to see it.”

My goal is to re-create what was magical for me, to find that aha moment.

—Sue Khim

With her app, Brilliant, she’s helping others see it that way too. Khim designed it to shatter the notion that the subject is intimidating or impenetrable. Through novel problems and games, Brilliant teaches math (as well as science and coding) to everyone from professionals looking for a career change to precocious 10-year-olds.

It does so by recasting math as a puzzle to be unlocked. “My goal is to re-create what was magical for me, to find that aha moment,” she says.

“That was my experience with math, but in talking to customers, I’ve learned that this is definitely not most people’s,” she says with a laugh.

In the beginning, Khim’s experience was a familiar one. After high school, she majored in math at the University of Chicago. But the entrepreneur in her called. She left after three years to launch Alltuition, which set out to connect students with financial aid. Brilliant followed two years later.

Born in South Korea, Sue Khim immigrated to America as a child and grew up in Chicago. She became a U.S. citizen shortly after launching Brilliant.

“We cover everything from fundamentals to advanced topics, and we offer this dash of magic to make it fun,” she says of Brilliant. “Without strong pedagogy, our aspirations would just be entertainment. But without the fun, we just come back to ‘math is scary.’ Balancing that is one of the most difficult parts of our job.”

In Brilliant, it’s fine to fail. A lot. “Part of what we’re trying to do is show you it’s OK to make mistakes,” says Khim. “That’s the opposite of what you learned at school, which is: There’s a cost to every mistake. But no matter what you do, you’re going to be given choices where there’s no obvious right answer, and you just have to figure it out.”

There’s more to Brilliant than math and logic. Take courses on neural networks, computer science, finance, and more.

Khim hears from all manner of satisfied math aficionados: a woman who tutors math students on three continents, an 80-year-old grandfather who solves its puzzles for fun at home. She’s gotten emails from university presidents and former cabinet members. But mostly, Brilliant’s fan base is people who want to keep learning.

Today, Brilliant has more than 9 million registered users and nearly 2 million people use the app each month. Those are numbers Khim likes a lot too.

*This question comes from German mathematician Carl Friedrich Gauss, who noticed if you put every number from 1 to 100 into two groups (1 to 50 and 51 to 100), you can add one number from each group to get 101: That is, 1+100=101, 2+99=101, and onward to 50+51=101. So, the total sum is 50 x 101, or 5050.