To play the yú (竽, an instrument) to make up numbers
To pass off inferior goods as superior ones; to pretend to have a talent and work alongside those who actually do have that talent
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老师让我们背诵课文，总有些同学滥竽充数 | Lǎoshī ràng wǒmen bèisòng kèwén, zǒng yǒu xiē tóngxué lànyúchōngshù
Whenever the teacher had us recite the text, there would always be some students who took advantage of the crowd and only pretended to recite the materials
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开展打假斗争，也包括把那些滥竽充数的劣质产品从消费领域中清除出去 | Kāizhǎn dǎjiǎ dòuzhēng, yě bāokuò bǎ nàxiē lànyúchōngshǔ de liè zhí chǎnpǐn cóng xiāofèi lǐngyù zhōng qīngchú chūqù
The effort to crack down on counterfeits includes removing from the market the shoddy goods that are being passed off as superior ones
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The 竽 (yú) is an ancient reed instrument that is made out of multiple bamboo pipes. People still play them in modern times, so you can look up some songs if you're interested in hearing what they sound like
《韩非子》(Hán Fēi Zǐ), a book of philosophy authored by 韩非 (Hán Fēi) during the Warring States Period (475 - 220 BC)
In ancient times, the kingdom of 齐国 (Qí Guó) was ruled by a king who loved music. The king especially loved to listen to musicians play the 竽 (yú, see story note) in large groups, and so he had in his employ a massive orchestra that consisted solely of 竽 players. He also enjoyed putting on extravagant shows of power and wealth, so whenever he held events, he would have the orchestra play for his visitors.
During this time, there was also a man named 南郭先生 (Nán Guō Xiān Shēng, or "Mr. Nanguo"). 南郭先生 was unskilled, uneducated, and lazy, and when he heard how the king liked to listen to music, he realized that he could exploit him and make a great deal of money. He went to court and explained that he was an expert 竽 player and that he was so great that "even plants who heard [his] song would sway in time to the rhythm." The king was delighted, and shortly after, 南郭先生 was playing in the orchestra alongside 300 other people.
The catch to all of this was that 南郭先生 couldn't actually play the 竽. Every single time there was a performance, he sat amongst the other musicians and just mimicked their actions. Still, he did this so well that people had no idea that he was deceiving them day after day, collecting wages and eating excellent food all the while.
南郭先生's ruse went on for several years until the king passed away. The new king also loved to listen to music, but he was different from his predecessor in one crucial way: he preferred to listen to people playing solo. As such, he ordered each and every one of the musicians to prepare for a solo performance. Immediately, 南郭先生 panicked, and that very night, he packed his things and fled the city.