Two different races, cultures, or religions under one roof add to the often-noted fireworks created by matrimony. According to the 2000 census, 4.9 percent of married couples in the United States represented “mixed races.” That's up from .7 percent in 1970. This huge increase in mixed marriages doesn't do away with many of the common problems that come up in today's multicultural marriage. If you are married to someone of a different race, religion, or ethnic group, your challenges arise from the different definitions each of you, and your respective in-laws, may have for what constitutes “normal” in a variety of situations. However, when you manage your differences well, you are also the recipient of many rewards.