Known for portraying Winnie Cooper in the coming-of-age television series "The Wonder Years," actress Danica McKellar has taken on several non-acting roles since then—including mathematician and New York Times best-selling author.
Growing up, the actress says she was always good at math. "I took the AP Calculus BC exam at the end of high school and scored a 5 which the highest score you could get," McKellar told CNBC's "On the Money" in an interview.
But that confidence soon disappeared when she entered college, in part because she thought she "didn't look the part" as someone who would major in mathematics. However, McKellar stuck with it and graduated summa cum laude from UCLA, where she co-authored the theorem Percolation and Gibbs States Multiplicity for Ferromagnetic Ashkin–Teller Models on Z2.
After graduating in 1998, McKellar went back to acting, but she also became an advocate for math and stem education. Over a decade ago, McKellar testified to a Congressional subcommittee about how to draw more women into science and math.
Her initial lack of confidence in college prompted her to write math books aimed at middle school and high school girls. Those works included her New York Times bestsellers "Math Doesn't Suck," "Kiss My Math," and "Girls Get Curves."
McKellar said she wanted young women to know "you don't have to be limited by the stereotypes in your head about who's going to be good at math." Even if you don't love math, McKellar recommended to keep at it.
"It exercises the problem solving part of your brain, which will help you better able to pursue your dreams, whatever they might be," the author and actress said.
"You don't have to choose between being fabulous and fun and being smart – they go hand in hand," she added.
To date McKellar has written 8 math books from toddler level to high school. Her latest is called "Do Not Open This Math Book" geared toward 6-8 year olds. Yet the book isn't just for kids, but their parents as well — especially those who are confused by or are not familiar with the 2010 Common Core teaching guidelines taught in most states.
At the end of the book, McKellar even wrote a 'new math' translation guide for parents. "A lot of the terms are different – there's no carrying and borrowing, there's grouping and ungrouping, regrouping. And there just shouldn't be such confusion," said the author.
In between writing math books, McKellar continues to act. She's had roles on "The Big Bang Theory," "West Wing" and she will star in her ninth Hallmark movie "Christmas at Grand Valley" later this month.
The movie is among nearly 40 Hallmark original Christmas movies this year, which will air across their two channels: Hallmark Channel and Hallmark Movies and Mysteries.
Since 2002, the network has produced 175 Christmas movies according to Megan Van Time, Hallmark's corporate communication coordinator.
McKellar says the movies are popular because people are looking for an escape.
"We need a break. We need to reconnect with core values and remember connection with family, and the importance of that, and the holidays are a great time for that and Hallmark is a great place for that."
Andthe actress experienced a reconnection while filming. Dan Lauria will be playing McKellar's father, but perhaps he is best known for his role as Jack Arnold in "The Wonder Years." The movie marks the first time in 25 years the two actors will be on screen together.
"Christmas at Grand Valley" airs December 21st on Hallmark Movies and Mystery.
On the Money airs on CNBC Saturdays at 5:30 am ET, or check listings for air times in local markets.