Final answer:
In 1970, approximately 66% of households in the United States consisted of nuclear families - married parents and children. However, this percentage has decreased over the years.
Step-by-step explanation:
In 1970, nuclear families were found in approximately 66% of households in the United States. This refers to households that consist of married parents and children as the core of the group. However, it is important to note that the percentage of nuclear families has decreased over the years, and other family structures such as single-parent households, cohabiting parents, and same-sex families have become more common.