Ben Folds has a proven method for making sure his solo shows take flight.

During the second half of each performance, the singer/songwriter/pianist invites the audience to write their requests on a piece of paper, fold them into an airplane and launch them on stage.

He then randomly chooses what to play among the requests.

“My personal rule is that I don’t play anything that wasn’t on the stage,” says Folds, who will perform with opener Ryan Lerman 9 p.m. Friday, April 21, at The Music Box at the Borgata Hotel Casino & Spa in Atlantic City.

However, the frontman of the Ben Folds Five also reserves the right to ignore certain asks.

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“I’ll pass on some stuff, if it’s going to make it a worse show,” he explains. “If it’s the last song — and someone asks for the fifth ballad in a row — or if it doesn’t make sense, I put those down and move on.”

With a catalog spanning hundreds of songs, Folds has needed to re-learn some tracks that seem obscure even to him. He assembled a book with lyrics and basic chords that covered his best-known material, but that proved inadequate to handle deep catalog requests, such as “Levi Johnston’s Blues,” a 2010 song co-written with Nick Hornby.

“People started asking for stuff that wasn’t in the book,” he says. “It put me to the test. I had to really brush up.”

Having composed his “Concerto for Piano and Orchestra,” Folds is even open to displaying his classical side by playing the first or third movement of the work. But it’s impossible to perform the entire piece without an orchestra on stage with him.

“A piano concerto rides back and forth between the orchestra,” he says. “It would be like me singing back up in the Supremes. It would go something like, ‘Ooh, ooh,’ and then there would be a break.”

For the North Carolina native — whose recent resume has included a reunion with the Ben Folds Five, an album with the Nashville Symphony Orchestra and a stint as a judge on the NBC reality competition “The Sing-Off” — performing solo feels right for now.

“It’s sort of home, in that’s what the songs are, and where, in a way, as a piano player and singer, I’m most comfortable,” Folds says. “It’s kind of the most ideal way for me to play, but that doesn’t mean I want to do it for years on end.

“I usually do it for three years at the most and then look for something different. At the end of three years, I go stir crazy and get sick of my bulls—.”

Having collaborated with everyone from Sara Bareilles and Regina Spektor to Weird Al and William Shatner, and now moving between pop and classical — sometimes even blending the two — Folds views these activities as being part of “one long, learning session.”

“When it comes to music, I don’t feel like it’s ever been settled — I don’t understand any of it,” he says. “I love the inside of an orchestra, and have continued to chip away at learning a lifetime of stuff about the orchestra.

“It’s kind of where my head is with learning — it’s not that different from an a cappella group or a rock band.”

Why Ben Folds did ‘The Sing-Off’

When Ben Folds got offered a spot as a judge on The Sing-Off, he thought it might be too “cheesy” to accept. But the challenge of evaluating a cappella performances in which the voices are intended to blend seamlessly into one appealed to him, so he said yes. He also had already demonstrated his affinity for the musical form, via his 2009 album “Ben Folds Presents: University A Cappella,” a collection of a cappella versions of his tunes by 14 college vocal groups and two of his own contributions.

When the South Jersey Area Wind Ensemble started up it was just a way for music professional…

“I enjoy that kind of listening — it’s always been an interest of mine, sort of my producer half,” Folds says. “If you are moved by something, delving into the reasons why it’s working can throw off your emotional side.

“Having the ability to go back and forth and make sure something works is a challenge and very useful for people.”