There are several table tennis balls in the box, 25% of which are first-class products, a few fifths are second-class products, and the remaining 91 are third-class products. So, how many ping pong balls are in the box?
箱子里有乒乓球若干个，其中25%是一级品，五分之几是二级品，其余91个是三级品．那么，箱子里有乒乓球多少个．
<result>260</result>