23. When the cashier rang up a bill for 22 p. 85 k. for an album costing 6 r., a book costing 12 r., 9 boxes of colored pencils, and 15 rulers, the customer, although not knowing the cost of the pencils and rulers, immediately noticed that the cashier had made a mistake. What was the basis for his suspicion?
23. If a box of pencils costs $x$ k., and a ruler costs $-y$ k., then pencils and rulers cost $(9 x+15 y)$ k. On the other hand, they cost 22 p. 85 k. $-(6+12)$ p. $=4$ p. 85 k. Therefore, $9 x+15 y=485$. The obtained equation cannot be true for any natural values of $x$ and $y$, since the left side is divisible by 3, while the right side is not $(4+8+5=17)$.