Bus tickets in a certain city contain four numbers, U, V ,
Chapter 2, Problem 17(choose chapter or problem)
Bus tickets in a certain city contain four numbers, U, V , W, and X. Each of these numbers is equally likely to be any of the 10 digits 0, 1,..., 9, and the four numbers are chosen independently. A bus rider is said to be lucky if U + V = W + X. What proportion of the riders are lucky?
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