Library / /321 of 356

, 1998

Number theory Difficulty 3.0 AMC 10/12 Find the answer Canada

Two natural numbers, $p$ and $q$ , do not end in zero. The product of any pair, $p$ and $q$ , is a power of 10 (that is, $10, 100, 1000, 10\,000, \ldots$ ). If $p > q$ , the last digit of $p - q$ cannot be

(A) $1$ (B) $3$ (C) $5$ (D) $7$ (E) $9$

Want a route through all this instead of an archive? The track puts 2,604 problems in a working order, from Junior Challenge level to the IMO shortlist.

Source: CEMC, University of Waterloo, licensed CC-BY-NC-4.0. Statement reproduced verbatim; metadata (topic, difficulty) added by this project. Solutions are the publisher's, linked not copied.