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smc

algebra senior

Problem

A high school basketball game between the Raiders and Wildcats was tied at the end of the first quarter. The number of points scored by the Raiders in each of the four quarters formed an increasing geometric sequence, and the number of points scored by the Wildcats in each of the four quarters formed an increasing arithmetic sequence. At the end of the fourth quarter, the Raiders had won by one point. Neither team scored more than points. What was the total number of points scored by the two teams in the first half?
(A)
(B)
(C)
(D)
(E)
Solution
Let be the quarterly scores for the Raiders. We know because the sequence is said to be increasing. We also know that each of is an integer. We start by showing that must also be an integer. Suppose not, and say where , and . Then must all divide so for some integer . Then and we see that even if and , we get , which means that the only option for is . A quick check shows that even this doesn't work. Thus must be an integer. Let be the quarterly scores for the Wildcats. Let . Let . Then implies that , so . The Raiders win by one point, so If we get which means , which is not possible with the given conditions. If we get which means , which is also not possible with the given conditions. * If we get which means . Reducing modulo 6 we get . Since we get . Thus . It then follows that . Then the quarterly scores for the Raiders are , and those for the Wildcats are . Also . The total number of points scored by the two teams in the first half is . Note if you don't realize while taking the test that might not be an integer: since an answer is achieved through casework on the integer value of and since there is only one right answer, the proof of being an integer can be skipped on the test (it takes up time).
Final answer
E