Actress Danica McKellar, who played Winnie on “The Wonder Years,” urges girls to embrace math. (Deb Lindsey/For The Washington Post)

Here’s a math question for Danica McKellar, the actress best known as Winnie Cooper on the hit TV show “The Wonder Years”: What percentage of her time does she spend acting, and what percentage writing books encouraging tween and teen girls to tackle math?

“If you look at the entire year, I would say 25 percent acting and 75 percent math books,” McKellar says in a phone interview from her home in California.

She still acts, but would rather talk about her fourth math book aimed at girls in fifth through 12th grades, “Girls Get Curves: Geometry Takes Shape.”

The cover, which features the 37-year-old McKellar, purposely looks like a teen magazine. It has subheads such as “How do you attract guys?” and “8 self-esteem boosters.” Inside, in addition to detailed explanations of how to do geometric proofs there are stories about the lives of successful women.

McKellar is trying to show girls that you don’t have to be a “nerdy” to understand math. “You don’t have to choose between being the fun, fabulous girl and being the smart girl who knows what’s up,” she says. “You can do both. That’s my big message.”

A math major

McKellar should know — she was on “The Wonder Years” for six years. The show ended in 1993, the same year McKellar graduated from high school. She went to the University of California at Los Angeles, intending to study film, but took a math class because she had always done well in math in high school. She did so well that she even proved a new mathematical formula, also known as a theorem, with a professor and a classmate, called the Chayes-McKellar-Winn theorem. McKellar went on to graduate with a math degree. “I felt valued for something that had nothing to do with Hollywood,” she says. “It had everything to do with my mind and my brain.”

She wanted to show other girls that they didn’t have to love math, but they had to realize they could do it. “It feels like this is combining the two sides of myself, my love of math and my love of entertaining,” McKellar says of writing the math books. “I’m making entertaining math books.”

McKellar is proudest of making dry mathematical formulas easy to remember. She uses the armpits of snow angels, for instance, to explain angles. She advises students to remember that acute angles are smaller than 90 degrees because they are so little and cute, and obtuse angles are bigger than 90 degrees because they’re obese.

Speaking tour

On her book tours, McKellar’s audiences tend to be teachers, parents and kids. She says she’s surprised that people don’t want to talk about her television roles, but about math.

“People are really interested about the state of girls dumbing themselves down,” she says.

There will likely be a fifth book; McKellar says she’s gotten many requests from parents to write books for third-graders.

— Newsday