This article seems to have a good grasp of the current wall street crash.
From the article, “It was the easy trade. Borrow at 3 percent and make 6 percent or 8 percent or 10 percent. They liked it so much, they levered up. Meaning instead of just borrowing a dollar for every two dollars of assets they owned (which by the way, thanks to the 50-percent margin requirement, is the amount of leverage that you and I are allowed to buy stocks from these same firms), they borrowed 20 to 1, 30 to 1, and even 50 to 1, if they could get away with it. And man, it was a lucrative trade. So why not?”
Its worth a read.