Facebook mobile ads drove 175 million app downloads in ten months

"Facebook offered a clue Tuesday as to how it had built its mobile advertising business so quickly.
Deborah Liu, a product manager, told a conference that Facebook users had downloaded 175 million mobile apps since January after seeing ads for those apps in their news feeds.
Liu came up with the idea for such mobile app install ads. She spoke at the Appnation conference in San Francisco.
Facebook had not disclosed the number of app install downloads since April, when it said there had been 25 million installs in the first quarter. That means there were 150 million downloads in the seven months between April and October."
Source:  WSJ, 3rd December 2013