First, the reported statistic was that 25% of the homeless population are veterans, which is VERY different from the statistic you cite. Second, the reported stat is that veterans account for 11% of the general population, not that 11% of the general population is homeless. In fact, about 7% of persons living in the U.S. have been homeless at some point in their lives, but the number that is homeless at any given time is considerably lower. Third, there is no way to calculate the information you're asking for from the info you're citing, even if it were cited accurately.
Finally, the statistic that was recently reported is itself meaningless because it does not give any information about expected rates of homelessness among veterans or among the population segments most likely to enter the military.
FYI, here are a couple of useful links about homelessness, demographics, and risk factors:
http://www.medscape.com/viewarticle/481800http://medicine.jrank.org/pages/831/Homelessness.html