NEW YORK (CBSNewYork) – A subway car recently became a classroom for one father as he tried to relearn elementary school math to help his son who was struggling in third grade.

Denise Wilson was riding the subway home to Brooklyn at the end of a long day last week when she overheard two strangers sitting across from her.

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“He was just telling the guy, ‘I’m in my 40s and all of this is new to me, so I’ve got to re-learn this to teach my son because he failed a math test,’” she told CBS2’s Ali Bauman.

Fractions, said the father, as he flipped through worksheets in his lap.

“When I say I started tearing up, that warmed my heart. So I snapped a picture,” Wilson said.

She posted it on Facebook, writing a stranger responded, “I used to be a math teacher,” then started quizzing the father with his folder.

“Everything he got wrong or was confused about, he broke it down and corrected him,” she wrote.

Corey Simmons admits he’s never been much of a math student.

“It’s been about 30 years I’d say since I did fractions,” he told Bauman.

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But when Corey Jr. started struggling in third grade, it was time to revisit some old lessons.

“It doesn’t matter if you fail, it’s what you do after you fail,” he said.

The men eventually got off at different stops.

Simmons said, between all the numbers, he didn’t catch the math tutor’s name. Neither did Wilson, even though her post has been shared more than 40,000 times.

“It was just one person helping another, and I thought that was beautiful,” she said.

As for the fractions, Simmons said “we’re halfway there, but I wouldn’t say we mastered the whole fraction thing yet.”

But maybe math was the second-most important lesson he brought home from his train ride.

“You need help sometimes and you shouldn’t want to bite your tongue, to not ask for the help,” he said. “So don’t feel shy to ask someone for help, it’s OK.”

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It’s a lesson Corey Jr. already seems to have a good grasp on, thanks to dad.