xinyu04

摘要： Four dogs occupy the four corners of a square with side of length a. At the same time each dog starts walking at the same speed directly toward the do 阅读全文

摘要： A factory that produces tables and chairs is equipped with 10 saws, 6 lathes, and 18 sanding machines. It takes a chair 10 minutes on a saw, 5 minutes 阅读全文