Write a question about the following article: According to 2011 census of India, Kumbakonam had a population of 140,156 with a sex-ratio of 1,021 females for every 1,000 males, much above the national average of 929. A total of 12,791 were under the age of six, constituting 6,495 males and 6,296 females.The average literacy of the city was 83.21%, compared to the national average of 72.99%. There were a total of 9,519 workers, comprising 32 cultivators, 83 main agricultural labourers, 1,206 in house hold industries, 7,169 other workers, 1,029 marginal workers, 24 marginal cultivators, 45 marginal agricultural labourers, 212 marginal workers in household industries and 0 other marginal workers.
How many percent were illiterate?