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MathNet 2024-part-05 — 168 problems (EN–VI) Question 163

Math Olympiad Vault · MathNet 2024-part-05 — 168 problems (EN–VI)

Question 163

In the following expression, Melanie changed some of the plus signs to minus signs:
$$
1 + 3 + 5 + 7 + \dots + 97 + 99.
$$
When the new expression was evaluated, it was negative. What is the least number of plus signs that Melanie could have changed to minus signs?
(A) 14 (B) 15 (C) 16 (D) 17 (E) 18