Answer based on context:

Using 2010 data, there were 28,264 households out of which 31.2% had children under the age of 18 living with them, 28.0% were Marriage living together, 24.7% had a female householder with no husband present, and 45.5% were non-families. 38.6% of all households were made up of individuals and 10.8% had someone living alone who was 65 years of age or older. The average household size was 2.23 and the average family size was 2.98.

How many percent do not have children under the age of 18 living with them?
68.8