Solution: (1) Set up a supermarket to buy P kilograms of big cherries at Q yuan per kilogram.
PQ yuan is used to buy big cherries, but only P( 1-5%) Jin is left when it is sold, and the price per Jin is Q( 1+5%) yuan, so you can get P( 1-5%) after it is sold? Q (1+5%) = pq [1-(5%) 2] (yuan),