Answer based on context:

For about three centuries, the Qing dynasty had enforced—albeit with mixed success—a policy of segregating the non-Han peoples  on the frontier from Han Chinese. By the end of the 19th century, however, China faced the prospect of being parcelled out among the Western powers and Japan, each competing for its own sphere of influence in the country. On the northern frontier, Russian Empire was viewed by the Qing court as posing the greatest threat to its territorial integrity. In response, the Qing government adopted a different policy, the "New Administration" or "New Policies" , which called for the sinification of Mongolia through Chinese colonisation, the exploitation of Mongolia's natural resources , military training, and education. Many Mongols regarded the "New Policies" as a major threat to their traditional way of life, as was agreed to be preserved when they recognised authority of the Qing emperors, and began to seek independence. In July 1911 a group of Khalkha nobles persuaded the Jebtsundamba Khutuktu, the head of Mongolian Buddhism , that Mongolia must declare its independence from the Qing dynasty. They agreed to send a small delegation to Russia to obtain its assistance in this undertaking. In October 1911 revolution broke out in China, with one province after another declaring its independence from the Qing government. On 1 December 1911 Outer Mongolia declared independence, and established a theocracy under the Khutuktu. On 29 December he was installed as the Bogd Khaan  of Mongolia. This ushered in the Bogd Khaan era, which lasted from 1911 to 1919.

How many months after a group of Khalkha nobles persuaded the Jebtsundamba Khutuktu that Mongolia must declare its independence from the Qing dynasty did a revolution break out in China?
3