Sunday Times Teaser 2554 – Odd and Even
by Graham Smithers
Published: 4 September 2011 (link)
Roddy and Eve have a set of cards on which is written a consecutive sequence of whole numbers, one number on each card. Roddy challenges Oliver to choose two cards at random, promising a prize if the sum of the numbers is odd. Eve issues the same challenge, but offers a prize for an even sum. Oliver accepts the challenge that gives him the greater probability of winning. This probability is a whole number percentage and, when reversed, it gives the two-figure number of cards.
Whose challenge did Oliver accept and how many cards are there?