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prealgebra intermediate

Problem

At a dance party a group of boys and girls exchange dances as follows: The first boy dances with girls, a second boy dances with girls, and so on, the last boy dancing with all the girls. If represents the number of boys and the number of girls, then:
(A)
(B)
(C)
(D)
Solution
After inspection, we notice a general pattern: the boy dances with girls. Since the last boy dances with all the girls, there must be four more girls than guys. Therefore, the equation that relates them is
Final answer
C