During the 1960s, median family incomes increased by over 33%, while per capita expenditures on recreation and meals grew by over 40%. From 1959 to 1969, median family income (in 1984 dollars) increased from $19,300 to $26,700. By 1969, 79.6% of all households owned at least one car, 82.6% owned a refrigerator or freezer, 79% owned a black and white television set, 31.9% owned a color television set, and 70% owned a washing machine. Leisure time also increased. By 1970, it was estimated that the average workingman in America had 140 days off work each year. US work hours fell by 10.7% between 1950 and 1979, though the decline was still around half that of Western Europe.

Based on the above article, answer a question. How many less people owned a washing machine than a black and white television set, in percentage?
9