By 1921, the Bolsheviks were winning the Russian Civil War and foreign troops were beginning to withdraw, yet Bolshevik leaders continued to keep tight control of the economy through the policy of War Communism. After years of economic crises caused by World War I and the Russian Civil War, the Bolshevik economy started to collapse. Industrial output had fallen dramatically. It is estimated that the total output of mines and factories in 1921 was 20 percent of the pre-World War I level, with many crucial items suffering an even more drastic decline. Production of cotton, for example, had fallen to 5 percent and iron to 2 percent of the pre-war level, and this coincided with droughts in 1920 and 1921 and the Russian famine of 1921. Discontent grew among the Russian populace, particularly the peasantry, who felt disadvantaged by Communist grain requisitioning . They resisted by refusing to till their land. In February 1921, more than 100 peasant uprisings took place. The workers in Petrograd were also involved in a series of strikes, caused by the reduction of bread rations by one third over a ten-day period.
Question: How much have the output of mines drop compared to pre world war 1?
Answer: 20 percent