Learn about subtraction with the San Diego Zoo’s famous baby pandas       Hua Mei was the first giant panda cub born in the United States that survived more than a few days. She was born at the San Diego Zoo, and four years later her mother had another baby, Mei Sheng. Hua Mei and her brother, Mei Sheng, spend their days climbing on logs, lounging in trees, and eating bamboo.             A lot of things the pandas do can be thought of in terms of subtraction. Young readers follow the famous cubs as they grow from tiny infants to big, bouncing pandas and learn about subtraction along the way.