2009 AMC 10B Problem 1

If Jane buys $b$ bagels, she buys $5-b$ muffins, for a total of $$50(5-b)+75b = 250+25b$$ cents. This is a whole number of dollars when $250+25b$ is a multiple of $100,$ that is, when $25b\equiv50\pmod{100},$ or $b\equiv2\pmod4.$ The only value with $0\le b\le5$ is $b=2.$ Thus, the correct answer is B.