Copyright © University of Cambridge. All rights reserved.
'Scratch Cards' printed from http://nrich.maths.org/
Mail order companies often send a scratch card with their
catalogue. These cards are used to encourage people to order from
the catalogue by offering a free prize. You have to uncover three
of the numbers by scratching off the cover and revealing the number
under three of the circles. Of course the numbers under the circles
are randomly placed. If the numbers add up to more than fifteen you
win a prize. What is the probability of winning a prize?