NATIONAL HARBOR, Md. – Apparently, it wasn’t the words that tripped up Marblehead Community Charter School seventh-grader Mitchell Robson. It was the math that did him in.Robson, the winner of the Daily Item Regional Spelling Bee that was held in April at Lynn City Hall Auditorium, was vying for the Scripps National Spelling Bee championship at the Gaylord National Resort and Convention Center Tuesday and Wednesday, and had hoped to go onto the final rounds today and tonight.After going through a preliminary test Tuesday, Robson, one of 285 spellers who entered the competition, endured two rounds during the day Wednesday. In the second round, he correctly spelled “implement,” which is both a noun (a tool) or a verb (to put a plan into action). And in the third round later in the day, Robson gave the correct spelling of “Pythagorean,” a mathematical term.Immediately after the third round, the event’s organizers applied a “maximum of 50” standard to all remaining spellers’ scores that had been accrued during the preliminaries – which also included a preliminary multiple choice test. Two points were awarded for correctly spelled words in Round 2; and three points in Round 3. The rest were accrued during the preliminary test.Spellers’ scores were plotted on a chart and the first 50 moved on, with the rest eliminated.