FREMONT — Marianna Mao was about 9 when she entered her first major math competition, facing students from three states. She did well enough to have her name mentioned in a newspaper.

Four years later, she decided to study for the Advanced Placement calculus exam on her own. Then an eighth-grader, she scored a perfect 5 on the college-level exam.

Today, at age 15, the Mission San Jose High School student is a member of the first U.S. team to compete in the China Girls Mathematical Olympiad, to be held next month in central China.

Eight girls — four each from the western and eastern halves of the United States — have been selected to represent the country.

To prepare, the girls are spending the next two weeks at the University of Texas in Dallas, where they've been studying algebra for three hours each morning and geometry for another three hours each afternoon.

"We're all really close-knit by now," Mao said Wednesday, after about a week with the group.

"It's the United States' first year at this event, so we all want to do well," she added.

Founded in 2002 as a contest for East Asian countries and Russia, the China Girls Mathematical Olympiad recently opened up the competition to students from the United States, Canada, South Africa, Australia and other nations.

The eight Americans chosen to represent the United States were among the top female contenders at the 2006 USA Mathematical Olympiad, a competition open to boys and girls living in the United States.

Six organizations joined together to sponsor the U.S. team's trip to China.

Nancy Stryble, director of corporate relations for the Berkeley-based Mathematical Sciences Research Institute, said the center chose to be a sponsor to encourage more women to pursue math and science education.

"This is a wonderful opportunity for a group of very bright girls to further their education and also to be ambassadors for the U.S. in another country," she said.

Although women make up about half of the overall work force in America, only 27 percent have computer- or math-related jobs, according to the U.S. Department of Labor. About 7 percent of electrical and electronics engineers are women, as are 35 percent of chemists and materials scientists.

Mao, who is about to enter her junior year of high school, said she'll likely pursue studies in math or science in college. In addition to math competitions, she participates in science bowls and is on her school's speech-anddebate team.

A self-described "regular girl," Mao enjoys playing the piano, riding her bicycle, running, taking photographs and shopping in her spare time.

Regardless of how she'll fare at next month's Olympiad, Mao's parents said they're proud of what she's accomplished already.

"We just tell her, 'If you really want to do something, be serious. Work hard. If you don't want to participate, that's OK. But if you want it, study hard,'" said her mother, Lin Mao.

"I just tell her to do her best. If you do your best, you won't regret it, no matter what the outcome."