When Ben Catalfo, 16, took a look at this year’s Regents Geometry exam, he realized something just didn’t add up.

Now the East Setauket math wiz is pressuring state officials to correct the error he found on the exam.

Catalfo, a junior at Ward Melville High School, reviewed the exam two weeks ago while preparing to tutor geometry students, he said. He was working through the test, administered to students on June 16, when he was stumped by a multiple-choice question asking students to prove two triangles are mathematically similar.

According to the test’s answer key, Answer 2 was the correct choice. But Catalfo, who passed the Regents exam in the seventh grade, found that none of the answers were correct.

Catalfo went over the problem “again and again.” He had his father, Anthony Catalfo, who works as a math tutor, check his work.

They came to the same conclusion and sought backup.

Catalfo consulted William Bernhard, his former principal at P.J. Gelinas Junior High School, who is also an adjunct math lecturer at Stony Brook University. Bernhard concluded Catalfo was right, and alerted the state Education Department.

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“I was in shock that there was another error,” Bernhard said. The department previously acknowledged two other questions out of 36 on the assessment had more than one correct answer. Officials told Bernhard they were aware of the situation and would not change how the question would be scored.

Emily DeSantis, an Education Department spokeswoman, has said the agency has done its best to respond to concerns voiced over the geometry exam.

“We have thoroughly vetted all concerns raised by educators regarding the questions on this exam and found that, with the exception of two questions for which we issued a notice to schools, all other questions on the exam are fair and each appropriately measures a geometry standard,” DeSantis said in a previous statement.

Newsday previously reported Catalfo’s findings and the state’s response in a story about declining student performance on the revamped geometry exam.

But Bernhard and Catalfo still believe more students deserved to pass.

On Monday, Catalfo created an online petition demanding the question be marked correct for all students. It’s been signed by nearly 400 people as of Tuesday afternoon.

It was no surprise to Bernhard that Catalfo would be the one to find the error. The 16-year-old is serious about math.

In the fifth grade, while most of his peers were memorizing multiplication tables, Catalfo enrolled in algebra at the junior high school. He completed trigonometry the following year and then geometry.

Catalfo will study differential equations next year, a course that’s typically taken by juniors in college, Bernhard said.

“I just get so excited thinking about math and working on problems,” Catalfo said.

He and his father work on problems in their free time. Notebooks half-filled with proofs and equations are strewn across their living room, Catalfo said.

His passion for math is partly why he created the petition, which has been commented on by dozens of people.

“I teach geometry and I want my students to be able to take a fair and mistake-free assessment,” one person wrote in the comments section of the petition.

A frustrated parent wrote: “My child didn’t take this one but it could have just as easily been his Regents that had this mistake. Why not right the wrong?”

Ben Catalfo said he hopes the petition will pressure the state Education Department to “acknowledge they made a mistake.”

“The question is unfair because there are no correct answers,” he said. “There are some kids who failed by a very small margin and there are some kids who might be in summer school because of this.”