Hereditary Defects: Down Syndrome and Sickle Cell Anemia

Young scholars solve problems like the following examples: 1. If you have 10,000 women, age 30, who have babies and one in 900 of these births will result in a Down syndrome baby, how many will have this disease? 2. 5,000 babies are born; 2,000 to women age 20, 3,000 to women age 40. How many of each group will give birth to a Down syndrome baby?