Did this become the new Common Core math problem: If 13 principals place orders for school supplies, and they only receive 65% of what they paid for, where did the other 35% of the money go? Don’t try to work it out on pencil and paper, because the New York Times has provided the answer for you.

In Detroit’s crumbling schools, where the threat of insolvency means that basic repairs, supplies and even teachers are in short supply, 13 principals conspired with a vendor to defraud the system, siphoning away millions of dollars, federal agents and prosecutors charged on Tuesday.

The principals, including five who have retired and one who became a district administrator, ordered supplies like paper, workbooks and chairs from the vendor, and Detroit Public Schools paid the bills. The vendor then delivered only some of the supplies to the schools, and paid $908,518 in kickbacks to the principals, according to documents filed in Federal District Court in Detroit.

At a news conference, Barbara L. McQuade, the United States attorney for the Eastern District of Michigan, said the orders had totaled about $5 million, “and of that, we believe that $2.7 million was fraudulent.”

In a city run by Democrats for years, under the influence of Democratic policies for years, and having been bankrupted by Democrats and Democratic policies, the only thing that should be surprising here is that we didn’t see this sooner…

Just weeks ago, another Detroit principal and another vendor pleaded guilty in a similar kickback scheme, albeit at schools that were run by a state agency, not Detroit Public Schools. That case led indirectly, through a two-year investigation by the F.B.I., the I.R.S. and prosecutors, to the one announced Tuesday, officials said.

…oh.

Final math question: If 13 principals and 2 vendors defraud a public school system over the course of a decade, how quickly are the students screwed out of a decent education? The answer is “They were long before these revelations.”