In the Weekend Insider:  We take a look at the Texas Department of Transportation's math skills. A few years ago, the agency announced a $1 billion dollar accounting goof; this year, TxDOT announced an extra $2 billion for road projects. Does this windfall limit its chances of receiving additional funding next session? And Ross Ramsey explains what happens at Texas political conventions and whether we still need them. Read full versions of these stories in The New York Times and at texastribune.org.