Stage: 4 Challenge Level: 
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?
Probability. Combinatorics. Mathematical modelling. Population Dynamics. Calculus generally. biology. engineering. Real world. Combinations. Theoretical probability.
Published July 1998.
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