Library / /74 of 165

, 2017

Number theory Difficulty 1.0 Junior Find the answer United Kingdom

The number 'ab' is the two-digit number with units digit $b$ and tens digit $a$ . The digits $a$ and $b$ are distinct, and non-zero. What is the largest possible value of 'ab' $-$ 'ba'?

(A) $81$ (B) $72$ (C) $63$ (D) $54$ (E) $45$

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: UK Mathematics Trust, licensed © UK Mathematics Trust; past papers published free at ukmt.org.uk. Statement reproduced verbatim; metadata (topic, difficulty) added by this project. Solutions are the publisher's, linked not copied.